Catalyst for clarifying exhaust gas

ABSTRACT

To provide an exhaust gas purifying catalyst which can maintain the catalytic activity at a high level over a long time and can achieve satisfactory emission control performance, an exhaust gas purifying catalyst is prepared so as to contain a noble metal, a perovskite-type composite oxide represented by the following general formula (3), and theta-alumina and/or alpha-alumina: 
 
AB 1−m N m O 3   (3) 
wherein A represents at least one element selected from rare-earth elements and alkaline earth metals; B represents at least one element selected from Al and transition elements excluding rare-earth elements and noble metals; N represents a noble metal; and m represents an atomic ratio of N satisfying the following relation: 0&lt;m&lt;0.5.

TECHNICAL FIELD

The present invention relates to an exhaust gas purifying catalyst. Morespecifically, it relates to an exhaust gas purifying catalyst containinga perovskite-type composite oxide for use as an exhaust gas purifyingcatalyst.

BACKGROUND ART

Perovskite-type composite oxides each supporting a noble metal such asPt (platinum), Rh (rhodium), or Pd (palladium) have been known asthree-way catalysts which can simultaneously clean up carbon monoxide(CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained inemissions. Such perovskite-type composite oxides are represented by ageneral formula: ABO₃ and enable the supported noble metal tosatisfactorily exhibit its catalytic activity.

These perovskite-type composite oxides, however, undergo grain growththereby to have a decreased specific surface area in an atmosphere ofhigh temperature. The resulting catalysts can only contact with exhaustgas components in a shorter time and exhibit remarkably decreasedcatalytic performance in an operating environment at a high spacevelocity as in the case of exhaust gas purifying catalysts forautomobiles.

Accordingly, various attempts have been proposed to increase theirthermostability by allowing such a perovskite-type composite oxide to besupported by a thermostable composite oxide containing Ce (cerium)and/or Zr (zirconium) (for example, Japanese Laid-open (Unexamined)Patent Publications No. Hei 5-31367, No. Hei 5-220395, No. Hei 5-253484,No. Hei 6-210175, No. Hei 7-68175, and No. Hei 7-80311).

Even the perovskite-type composite oxide supported by the thermostablecomposite oxide containing Ce and/or Zr, however, shows remarkablydecreased catalytic performance in an atmosphere of high temperatureexceeding 900° C. to 1000° C.

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide an exhaustgas purifying catalyst which can maintain its catalytic performance at ahigh level over a long time and can achieve satisfactory emissioncontrol performance even in an atmosphere of high temperature.

The present invention provides an exhaust gas purifying catalystcontaining a noble metal, a perovskite-type composite oxide, and atleast one of theta-alumina and alpha-alumina.

The exhaust gas purifying catalyst of the present invention preferablycontains at least one of theta-alumina and alpha-alumina, and aperovskite-type composite oxide containing a noble metal.

The perovskite-type composite oxide containing a noble metal ispreferably supported by theta-alumina and/or alpha-alumina.

It is also preferred in the present invention that the perovskite-typecomposite oxide containing a noble metal is supported by at least onethermostable oxide selected from the group consisting of zirconiacomposite oxides represented by the following general formula (1), ceriacomposite oxides represented by the following general formula (2),SrZrO₃ and LaAlO₃:Zr_(1−(a+b))Ce_(a)R_(b)O_(2−c)  (1)wherein R represents at least one of alkaline earth metals andrare-earth elements excluding Ce; a represents an atomic ratio of Cesatisfying the following relation: 0.1≦a≦0.65; b represents an atomicratio of R satisfying the following relation: 0≦b≦0.55; [1−(a+b)]represents an atomic ratio of Zr satisfying the following relation:0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect,Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (2)wherein L represents at least one of alkaline earth metals andrare-earth elements excluding Ce; d represents an atomic ratio of Zrsatisfying the following relation: 0.2≦d≦0.7; e represents an atomicratio of L satisfying the following relation: 0≦e≦0.2; [1−(d+e)]represents an atomic ratio of Ce satisfying the following relation:0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.

In the present invention, at least one of theta-alumina andalpha-alumina supporting the perovskite-type composite oxide containinga noble metal, or the thermostable oxide supporting the perovskite-typecomposite oxide containing a noble metal is preferably prepared byincorporating at least one of theta-alumina and alpha-alumina, or athermostable oxide into a pre-crystallization composition before thecrystallization of the perovskite-type composite oxide containing anoble metal, in the production of the perovskite-type composite oxidecontaining a noble metal.

In such supporting, the catalyst preferably further comprises at leastone thermostable oxide selected from the group consisting of zirconiacomposite oxides represented by the following general formula (1), ceriacomposite oxides represented by the following general formula (2),theta-alumina, alpha-alumina, gamma-alumina, SrZrO₃ and LaAlO₃:Zr_(l−(a+b))Ce_(a)R_(b)O_(2−c)  (1)wherein R represents at least one of alkaline earth metals andrare-earth elements excluding Ce; a represents an atomic ratio of Cesatisfying the following relation: 0.1≦a≦0.65; b represents an atomicratio of R satisfying the following relation: 0≦b≦0.55; [1−(a+b)]represents an atomic ratio of Zr satisfying the following relation:0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect,Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (2)wherein L represents at least one of alkaline earth metals andrare-earth elements excluding Ce; d represents an atomic ratio of Zrsatisfying the following relation: 0.2≦d≦0.7; e represents an atomicratio of L satisfying the following relation: 0≦e≦0.2; [1−(d+e)]represents an atomic ratio of Ce satisfying the following relation:0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.

It is also preferred in the present invention that the perovskite-typecomposite oxide containing a noble metal is mixed with at least one oftheta-alumina and/or alpha-alumina.

In such mixing, at least one thermostable oxide selected from the groupconsisting of zirconia composite oxides represented by the followinggeneral formula (1), ceria composite oxides represented by the followinggeneral formula (2), gamma-alumina, SrZrO₃ and LaAlO₃ is preferablyfurther mixed:Zr_(1−(a+b))Ce_(a)R_(b)O_(2−c)  (1)wherein R represents at least one of alkaline earth metals andrare-earth elements excluding Ce; a represents an atomic ratio of Cesatisfying the following relation: 0.1≦a≦0.65; b represents an atomicratio of R satisfying the following relation: 0≦b≦0.55; [1−(a+b)]represents an atomic ratio of Zr satisfying the following relation:0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect,Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (2)wherein L represents at least one of alkaline earth metals andrare-earth elements excluding Ce; d represents an atomic ratio of Zrsatisfying the following relation: 0.2≦d≦0.7; e represents an atomicratio of L satisfying the following relation: 0≦e≦0.2; [1−(d+e)]represents an atomic ratio of Ce satisfying the following relation:0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.

The perovskite-type composite oxide containing a noble metal in thepresent invention is preferably represented by the general formula (3):AB_(1−m)N_(m)O₃  (3)wherein A represents at least one element selected from rare-earthelements and alkaline earth metals; B represents at least one elementselected from Al and transition elements excluding rare-earth elementsand noble metals; N represents a noble metal; and m represents an atomicratio of N satisfying the following relation: 0<m<0.5.

N in general formula (3) is preferably at least one selected from thegroup consisting of Rh, Pd, and Pt.

The perovskite-type composite oxide represented by the general formula(3) is preferably at least one selected from the group consisting ofRh-containing perovskite-type composite oxides represented by thefollowing general formula (4), Pd-containing perovskite-type compositeoxides represented by the following general formula (5), andPt-containing perovskite-type composite oxides represented by thefollowing general formula (6):A_(1−p)A′_(p)B_(1−q)Rh_(q)O₃  (4)wherein A represents at least one element selected from La, Nd, and Y;A′ represents Ce and/or Pr; B represents at least one element selectedfrom Fe, Mn, and Al; p represents an atomic ratio of A′ satisfying thefollowing relation: 0≦p<0.5; and q represents an atomic ratio of Rhsatisfying the following relation: 0<q≦0.8,AB_(1−r)Pd_(r)O₃  (5)wherein A represents at least one element selected from La, Nd, and Y; Brepresents at least one element selected from Fe, Mn, and Al; and rrepresents an atomic ratio of Pd satisfying the following relation:0<r≦0.5,A_(1−s)A′_(s)B_(1−t−u)B′_(t)Pt_(u)O₃  (6)wherein A represents at least one element selected from La, Nd, and Y;A′ represents at least one element selected from Mg, Ca, Sr, Ba, and Ag;B represents at least one element selected from Fe, Mn, and Al; B′represents at least one element selected from Rh and Ru; s represents anatomic ratio of A′ satisfying the following relation: 0<s≦0.5; trepresents an atomic ratio of B′ satisfying the following relation:0≦t<0.5; and u represents an atomic ratio of Pt satisfying the followingrelation: 0<u≦0.5.

In the present invention, at least one of theta-alumina andalpha-alumina is preferably represented by the following general formula(7):(Al_(1−g)D_(g))₂O₃  (7)wherein D represents La and/or Ba; and g represents an atomic ratio of Dsatisfying the following relation: 0≦g≦0.5.

It is preferred in the present invention that the zirconia compositeoxide comprises a zirconia composite oxide supporting Pt and/or Rh, theceria composite oxide comprises a ceria composite oxide supporting Pt,the theta-alumina comprises a theta-alumina supporting Pt and/or Rh, andthe gamma-alumina comprises a gamma-alumina supporting Pt and/or Rh.

The catalyst of the present invention preferably comprises a coatinglayer supported by a catalyst carrier, in which the coating layerincludes an outer layer constituting its surface layer, and an innerlayer arranged inside the outer layer, and at least one of the outerlayer and the inner layer comprises both at least one of theta-aluminaand alpha-alumina, and the perovskite-type composite oxide containing anoble metal.

The inner layer preferably comprises at least one of theta-alumina andalpha-alumina each supporting the perovskite-type composite oxidecontaining a noble metal.

The inner layer preferably comprises the thermostable oxide supportingthe perovskite-type composite oxide containing a noble metal.

Preferably, the inner layer comprises the Pd containing perovskite-typecomposite oxide.

The outer layer preferably comprises the Rh-containing perovskite-typecomposite oxide.

The Pt containing perovskite-type composite oxide is preferablycontained in the inner layer and/or the outer layer.

Preferably, the noble metal contained in the outer layer is Rh and/orPt, and the noble metal contained in the inner layer is at least Pd.

Preferably, the inner layer comprises the ceria composite oxidesupporting theta-alumina and Pt, and the outer layer comprises at leastone thermostable oxide selected from the group consisting of thezirconia composite oxide supporting Pt and Rh, the ceria composite oxidesupporting Pt, and theta-alumina supporting Pt and Rh.

The exhaust gas purifying catalyst of the present invention preferablyfurther comprises at least one of sulfates, carbonates, nitrates, andacetates of Ba, Ca, Sr, Mg, or La.

The exhaust gas purifying catalyst of the present invention allows thenoble metal to maintain its catalytic activity at a high level over along time and can achieve satisfactory emission control performance evenin an atmosphere of high temperature exceeding 900° C. to 1000° C.

BEST MODE FOR CARRYING OUT THE INVENTION

The exhaust gas purifying catalyst of the present invention comprises anoble metal, perovskite-type composite oxides and at least one oftheta-alumina and alpha-alumina.

The exhaust gas purifying catalyst of the present invention has only tocomprise these components, i.e., the noble metal, the perovskite-typecomposite oxide, and at least one of theta-alumina and alpha-alumina.These components may be mixed. Alternatively, the noble metal may besupported by the perovskite-type composite oxide and/or at least one oftheta-alumina and alpha-alumina. Preferably, the catalyst comprises atleast one of theta-alumina and alpha-alumina, and a perovskite-typecomposite oxide containing a noble metal.

The perovskite-type composite oxide containing a noble metal for use inthe present invention are composite oxides each having a perovskitestructure represented by the general formula: ABO₃ and include, forexample, perovskite-type composite oxides each comprising a noble metalas a constituent and perovskite-type composite oxides each supporting anoble metal.

The perovskite-type composite oxide each comprising a noble metal as aconstituent are represented by, for example, the following generalformula (3):AB_(1−m)N_(m)O₃  (3)wherein A represents at least one element selected from rare-earthelements and alkaline earth metals; B represents at least one elementselected from Al and transition elements excluding rare-earth elementsand noble metals; N represents one or more noble metals; and mrepresents an atomic ratio of N satisfying the following relation:0<m<0.5.

In general formula (3), examples of the rare-earth elements representedby A include Sc (scandium), Y (yttrium), La (lanthanum), Ce (cerium), Pr(praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu(europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho(holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

Examples of the alkaline earth metals represented by A include Be(beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium),and Ra (radium). These alkaline earth metals can be used alone or incombination.

Examples of the transition elements represented by B excluding therare-earth elements and the noble metals in general formula (3) includeelements having atomic numbers of 22 (Ti) through 30 (Zn), atomicnumbers of 40 (Zr) through 48 (Cd), and atomic numbers of 72 (Hf)through 80 (Hg) in the Periodic Table of Elements (IUPAC, 1990) exceptfor the noble metals having atomic numbers of 44 through 47 and 76through 78. These transition elements can be used alone or incombination.

Preferred examples of B, i.e., Al and the transition elements excludingthe rare-earth elements and the noble metals, include Ti (titanium), Cr(chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu(copper), Zn (zinc), and Al (aluminum).

Examples of the noble metal represented by N in general formula (3)include Ru (ruthenium), Rh (rhodium), Pd (palladium), Ag (silver), Os(osmium), Ir (iridium), and Pt (platinum), of which Rh, Pd, and Pt arepreferred. These noble metals can be used alone or in combination.

The atomic ratio m satisfies the relation: 0<m<0.5. Namely, N is anessential component, the atomic ratio of N is less than 0.5, and theatomic ratio of B is 0.5 or more.

These perovskite-type composite oxides can be prepared according to anysuitable procedure for the production of composite oxides. Examplesthereof include a coprecipitation process, a citrate complex process,and an alkoxide process, without being limited to any particularprocess.

In the coprecipitation process, for example, an aqueous mixed saltsolution containing salts of the above-mentioned elements in apredetermined stoichiometric ratio is initially prepared. The aqueousmixed salt solution is coprecipitated by the addition of a neutralizingagent, and the resulting coprecipitate is dried and heat-treated.

Examples of the salts of the elements include inorganic salts such assulfates, nitrates, chlorides, and phosphates; and organic salts such asacetates and oxalates. The aqueous mixed salt solution can be prepared,for example, by adding the salts of the elements to water in suchproportions as to establish a predetermined stoichiometric ratio andmixing them with stirring.

Subsequently, the aqueous mixed salt solution is coprecipitated byadding the neutralizing agent thereto. The neutralizing agent includes,for example, ammonia; organic bases including amines such astriethylamine and pyridine; and inorganic bases such as sodiumhydroxide, potassium hydroxide, potassium carbonate, and ammoniumcarbonate. The neutralizing agent is added dropwise to the aqueous mixedsalt solution so that the solution after the addition of theneutralizing agent has a pH of about 6 to 10.

The resulting coprecipitate is, where necessary, washed with water, isdried typically by vacuum drying or forced-air drying and is thenheat-treated at about 500° C. to 1000° C., and preferably at about 600°C. to about 950° C., for example. The perovskite-type composite oxidecan thus be prepared.

In the citrate complex process, for example, an aqueous citric acidsolution in a slightly excess amount with respect to the stoichiometricratio of the respective elements is added to the salts of the respectiveelements to prepare an aqueous citrate mixed salt solution, the aqueouscitrate mixed salt solution is evaporated to dryness to form a citratecomplex of the respective elements, and the resulting citrate complex isprovisionally baked and is heat-treated.

The same as listed above can be used as the salts of the elementsherein. The aqueous citrate mixed salt solution can be prepared byinitially preparing an aqueous mixed salt solution by the aboveprocedure and adding an aqueous solution of citric acid to the aqueousmixed salt solution.

Then, the aqueous citrate mixed salt solution is evaporated to drynessto form a citrate complex of the respective elements. The evaporation todryness is carried out at such a temperature at which the formed citratecomplex is not decomposed, for example, at room temperature to about150° C., thereby to remove the fluid immediately. The citrate complex ofthe elements is thus obtained.

The formed citrate complex is then provisionally baked and is thenheat-treated. The provisional baking may be carried out by heating at250° C. to 350° C. in vacuum or in an inert atmosphere. Theprovisionally baked article is then heat-treated, for example, at about500° C. to 1000° C., and preferably at about 600° C. to 950° C. toobtain the perovskite-type composite oxide comprising a noble metal as aconstituent.

In the alkoxide process, for example, a mixed alkoxide solutioncontaining alkoxides of the respective elements excluding the noblemetals in the stoichiometric ratio is prepared, and the mixed alkoxidesolution is precipitated on hydrolysis by adding an aqueous solutioncontaining salts of the noble metals thereto, and the resultingprecipitate is dried and is heat-treated.

Examples of the alkoxides of the respective elements include alcholateseach comprising the element and an alkoxy such as methoxy, ethoxy,propoxy, isopropoxy, or butoxy; and alkoxyalcholates of the respectiveelements represented by the following general formula (8):E[OCH(R¹)—(CH₂)_(i)—OR²]_(j)  (8)wherein E represents the element; R¹ represents a hydrogen atom or analkyl group having 1 to 4 carbon atoms; R² represents an alkyl grouphaving 1 to 4 carbon atoms; i represents an integer of 1 to 3; and jrepresents an integer of 2 to 4.

More specific examples of the alkoxyalcholates include methoxyethylate,methoxypropylate, methoxybutylate, ethoxyethylate, ethoxypropylate,propoxyethylate, and butoxyethylate.

The mixed alkoxide solution can be prepared, for example, by adding thealkoxides of the respective elements to an organic solvent so as toestablish the stoichiometric ratio and mixing them with stirring. Theorganic solvent is not specifically limited, as long as it can dissolvethe alkoxides of the respective elements. Examples of such organicsolvents include aromatic hydrocarbons, aliphatic hydrocarbons,alcohols, ketones, and esters. Among these organic solvents, aromatichydrocarbons such as benzene, toluene, and xylene are preferred.

Subsequently, the mixed alkoxide solution is precipitated by adding anaqueous solution containing salts of the noble metals in a predeterminedstoichiometric ratio. Examples of the aqueous solution containing saltsof the noble metals include aqueous nitrate solution, aqueous chloridesolution, aqueous hexaammine chloride solution, aqueous dinitrodiamminenitrate solution, hexachloro acid hydrate, and potassium cyanide salt.

The resulting precipitate is then dried typically by vacuum drying orforced-air drying and is heat-treated, for example, at about 500° C. to1000° C., and preferably at about 500° C. to 850° C. Thus, theperovskite-type composite oxide comprising a noble metal as aconstituent can be prepared.

In the alkoxide process, the perovskite-type composite oxide comprisinga noble metal as a constituent may be alternatively prepared in thefollowing manner. A solution containing organometal salts of the noblemetals is added to the mixed alkoxide solution to obtain a homogenousmixed solution. The homogenous mixed solution is precipitated by addingwater thereto. The resulting precipitate is dried and is heat-treated.

Examples of the organometal salts of the noble metals include carboxylicacid salts of the noble metals derived from, for example, acetates orpropionates; and metal chelate complexes of the noble metals derivedfrom, for example, β-diketone compounds or β-ketoester compoundsrepresented by the following general formula (9) and/or β-dicarboxylicester compounds represented by the following general formula (10).R³COCHR⁵COR⁴  (9)wherein R³ represents an alkyl group having 1 to 6 carbon atoms, afluoroalkyl group having 1 to 6 carbon atoms or an aryl group; R⁴represents an alkyl group having 1 to 6 carbon atoms, a fluoroalkylgroup having 1 to 6 carbon atoms, an aryl group or an alkyloxy grouphaving 1 to 4 carbon atoms; and R⁵ represents a hydrogen atom or analkyl group having 1 to 4 carbon atoms,R⁷CH(COOR⁶)²  (10)wherein R⁶ represents an alkyl group having 1 to 6 carbon atoms; and R⁷represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

In the above-mentioned general formulas (9) and (10), examples of thealkyl groups each having 1 to 6 carbon atoms as R³, R⁴, and R⁶ includemethyl, ethyl, propyl, isopropyl, n-butyl, s-butyl, t-butyl, t-amyl, andt-hexyl. Examples of the alkyl groups each having 1 to 4 carbon atoms asR⁵ and R⁷ include methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl,and t-butyl. The fluoroalkyl groups each having 1 to 6 carbon atoms asR³ and R⁴ include, for example, trifluoromethyl. The aryl groups as R³and R⁴ include, for example, phenyl. The alkyloxy group having 1 to 4carbon atoms as R⁴ includes, for example, methoxy, ethoxy, propoxy,isopropoxy, n-butoxy, s-butoxy, and t-butoxy.

More specific examples of the β-diketone compounds include2,4-pentanedione, 2,4-hexanedione, 2,2-dimethyl-3,5-hexanedione,1-phenyl-1,3-butanedione, 1-trifluoromethyl-1,3-butanedione,hexafluoroacetylacetone, 1,3-diphenyl-1,3-propanedione, anddipivaloylmethane. Examples of the β-ketoester compounds include methylacetoacetate, ethyl acetoacetate, and t-butyl acetoacetate. Examples ofthe β-dicarboxylic ester compounds include dimethyl malonate and diethylmalonate.

The solution containing the organometal salts of the noble metals can beprepared, for example, by adding the organometal salts of the noblemetals to an organic solvent so as to establish the stoichiometric ratioand mixing them with stirring. The same as listed above can be used asthe organic solvent herein.

Thus-prepared solution containing the organometal salts of the noblemetals is mixed with the mixed alkoxide solution to prepare thehomogenous mixed solution, and the homogenous mixed solution isprecipitated by adding water thereto. The resulting precipitate is driedtypically by vacuum drying or forced-air drying and is then heat-treatedat about 400° C. to 1000° C., and preferably at about 500° C. to 850° C.Thus, the perovskite-type composite oxide can be prepared.

Examples of the perovskite-type composite oxide supporting a noble metalinclude perovskite-type composite oxides represented by the followinggeneral formula (3-1) each of which supports a noble metal.ABO₃  (3-1)wherein A represents at least one element selected from rare-earthelements and alkaline earth metals; and B represents at least oneelement selected from Al and transition elements excluding therare-earth elements and the noble metals.

The same as listed above can be used as the rare-earth elements and thealkaline earth metals represented by A, and Al and the transitionelements represented by B excluding the rare-earth elements and thenoble metals in the general formula (3-1).

These perovskite-type composite oxides can be prepared by a suitableprocess for the production of composite oxides such as a coprecipitationprocess, a citrate complex process, or an alkoxide process, as in theabove processes. In the alkoxide process, the mixed alkoxide solutionmay be hydrolyzed by adding water thereto.

The noble metal can be supported by the resulting perovskite-typecomposite oxide according to any known process, without being limited toa particular process. The noble metal can be supported, for example, bypreparing a salt solution containing the noble metals, impregnating theperovskite-type composite oxide with the salt-containing solution andthen baking the impregnated composite oxide. The amount of the noblemetals to the perovskite-type composite oxide is, for example, 20 partsby weight or less, and preferably 0.5 parts to 5 parts by weight to 100parts by weight of the perovskite-type composite oxide.

Of the perovskite-type composite oxides each containing a noble metal,the perovskite-type composite oxides each comprising a noble metal as aconstituent are preferably used. When the noble metal is Rh, aRh-containing perovskite-type composite oxide represented by thefollowing general formula (4) is typically preferably used as theperovskite-type composite oxide containing a noble metal in the presentinvention:A_(1−p)A′_(p)B_(1−q)Rh_(q)O₃  (4)wherein A represents at least one element selected from La, Nd, and Y;A′ represents Ce and/or Pr; B represents at least one element selectedfrom Fe, Mn, and Al; p represents an atomic ratio of A′ satisfying thefollowing relation: 0≦p<0.5; and q represents an atomic ratio of Rhsatisfying the following relation: 0<q≦0.8.

When the noble metal is Pd, a Pd containing perovskite-type compositeoxide represented by the following general formula (5) is preferablyused:AB_(1−r)Pd_(r)O₃  (5)wherein A represents at least one element selected from La, Nd, and Y; Brepresents at least one element selected from Fe, Mn, and Al; and rrepresents an atomic ratio of Pd satisfying the following relation:0<r<0.5.

When the noble metal is Pt, a Pt containing perovskite-type compositeoxide represented by the following general formula (6) is preferablyused:A_(1−s)A′_(s)B_(1−t−u)B′_(t)Pt_(u)O₃  (6)wherein A represents at least one element selected from La, Nd, and Y;A′ represents at least one element selected from Mg, Ca, Sr, Ba, and Ag;B represents at least one element selected from Fe, Mn, and Al; B′represents at least one element selected from Rh and Ru; s represents anatomic ratio of A′ satisfying the following relation: 0<s≦0.5; trepresents an atomic ratio of B′ satisfying the following relation:0≦t<0.5; and u represents an atomic ratio of Pt satisfying the followingrelation: 0<u≦0.5.

The theta-alumina for use in the present invention is a kind ofintermediate (transitional) alumina until it is transferred toalpha-alumina, and has a theta phase as its crystal phase. Thetheta-alumina can be prepared, for example, by heat-treating acommercially available active alumina (gamma-alumina) at 900° C. to1100° C. in the air for 1 to 10 hours.

The theta-alumina is available, for example, by heat-treating SPHERALITE531P (a trade name of a gamma-alumina produced by PROCATALYSE) at 1000°C. in the air for 1 to 10 hours.

The alpha-alumina for use in the present invention has an alpha phase asits crystal phase and includes, for example, AKP-53 (a trade name of ahigh-purity alumina produced by Sumitomo Chemical Industries Co., Ltd.).

Such an alpha-alumina can be prepared, for example, by an alkoxideprocess, a sol-gel process, or a coprecipitation process.

At least one of theta-alumina and alpha-alumina for use in the presentinvention may comprise La and/or Ba. Namely, one represented by thefollowing general formula (7) is preferably used:(Al_(1−g)D_(g))₂O₃  (7)wherein D represents La and/or Ba; and g represents an atomic ratio of Dsatisfying the following relation: 0≦g≦0.5.

D represents La and/or Ba, and the atomic ratio of D represented by granges from 0 to 0.5. Namely, La and/or Ba is not an essential componentbut is an optional component which may be contained optionally, and theatomic ratio thereof is, if contained, 0.5 or less. If the atomic ratioof La and/or Ba exceeds 0.5, the crystal phase may not maintain itstheta phase and/or alpha phase.

The theta-alumina and/or alpha-alumina is allowed to comprise La and/orBa, for example, by appropriately controlling a baking temperature in aproduction process using aluminum oxide and a salt or alkoxide of Laand/or Ba as in a production method of the zirconia composite oxidedescribed later. Alternatively, the theta-alumina and/or alpha-aluminacomprising La and/or Ba can be obtained, for example, by impregnatingtheta-alumina and/or alpha-alumina with a solution of a salt of Laand/or Ba, followed by drying and baking.

At least one of theta-alumina and alpha-alumina has a specific surfacearea of preferably 5 m²/g or more, or more preferably 10 m²/g or more.In particular, theta-alumina has a specific surface area of preferably50 m²/g to 150 m²/g, or more preferably 100 m²/g to 150 m²/g. Aplurality of theta-alumina and/or alpha-alumina having different atomicratios of La and/or Ba can be used in combination.

As is described above, the exhaust gas purifying catalyst of the presentinvention is not specifically limited, as long as it comprises the noblemetal, the perovskite-type composite oxide and at least one oftheta-alumina and alpha-alumina. In a preferred embodiment, the exhaustgas purifying catalyst comprises at least one of theta-alumina andalpha-alumina, and the perovskite-type composite oxide containing anoble metal. This embodiment can be any of an embodiment in which theperovskite-type composite oxide containing a noble metal is supported byat least one of theta-alumina and alpha-alumina, and an embodiment inwhich the perovskite-type composite oxide containing a noble metal ismixed with at least one of theta-alumina and alpha-alumina.

In the embodiment in which the perovskite-type composite oxidecontaining a noble metal is supported by at least one of theta-aluminaand alpha-alumina (hereinafter referred to as “supporting embodiment”),the amount of at least one of theta-alumina and alpha-alumina to supportthe perovskite-type composite oxide containing a noble metal is notspecifically limited and is, for example, 0.5 parts to 20 parts byweight, and preferably 0.5 parts to 10 parts by weight, to 1 part byweight of the perovskite-type composite oxide containing a noble metal.If the amount of at least one of theta-alumina and alpha-alumina is lessthan the above-specified range, the perovskite-type composite oxidecontaining a noble metal may not be sufficiently effectively dispersedand may fail to prevent grain growth in an atmosphere of hightemperature. A proportion of at least one of theta-alumina andalpha-alumina exceeding the above-specified range may invitedisadvantages in cost and production.

The perovskite-type composite oxide containing a noble metal may besupported by at least one of theta-alumina and alpha-alumina in thefollowing manner, without being limited to a particular process.Specifically, at least one of theta-alumina and alpha-alumina isincorporated into a pre-crystallization composition in the course of theproduction of the perovskite-type composite oxide containing a noblemetal before the crystallization thereof, and the resulting mixture isheat-treated. This allows the pre-crystallization composition tocrystallize thereby to allow at least one of theta-alumina andalpha-alumina to support the perovskite-type composite oxide containinga noble metal.

More specifically, a powder of at least one of theta-alumina andalpha-alumina may be mixed, for example, with a mixed solution(pre-crystallization composition) containing elementary componentsconstituting the perovskite-type composite oxide containing a noblemetal or with the resulting precipitate (pre-crystallizationcomposition), and the resulting mixture is heat-treated.

When the perovskite-type composite oxide comprising a noble metal as aconstituent is prepared by the coprecipitation process, the powder of atleast one of theta-alumina and alpha-alumina may be added, for example,to the prepared aqueous mixed salt solution (pre-crystallizationcomposition), the resulting coprecipitate (pre-crystallizationcomposition), or a dried product thereof (pre-crystallizationcomposition) and then heat-treated.

When the perovskite-type composite oxide comprising a noble metal as aconstituent is prepared by the citrate complex process, the powder of atleast one of theta-alumina and alpha-alumina may be added, for example,to the prepared aqueous citrate mixed salt solution (pre-crystallizationcomposition), the resulting citrate complex (pre-crystallizationcomposition), or a provisionally baked product thereof(pre-crystallization composition) and then heat-treated.

When the perovskite-type composite oxide comprising a noble metal as aconstituent is prepared by the alkoxide process, the powder of at leastone of theta-alumina and alpha-alumina may be added, for example, to theprepared mixed alkoxide solution (pre-crystallization composition) orhomogenous mixed solution (pre-crystallization composition), theresulting precipitate (pre-crystallization composition), or a driedproduct thereof (pre-crystallization composition) and then heat-treated.

Among the above-mentioned processes, preferred is the process in whichthe powder of at least one of theta-alumina and alpha-alumina is addedby the alkoxide process in the course of the production of theperovskite-type composite oxide comprising a noble metal as aconstituent and is heat-treated.

The exhaust gas purifying catalyst of the present invention according tothe supporting embodiment may further be mixed with at least onethermostable oxide selected from the group consisting of zirconiacomposite oxides, ceria composite oxides, theta-alumina, alpha-alumina,gamma-alumina, SrZrO₃ and LaAlO₃. By mixing with any of thesethermostable oxides, the perovskite-type composite oxide containing anoble metal can have further improved thermostability. This easilyenables the exhaust gas purifying catalyst of the present invention tobe used in a very severe atmosphere of high temperature such as inmanifold converters.

The zirconia composite oxides are represented by the following generalformula (1):Zr_(1−(a+b))Ce_(a)R_(b)O_(2−c)  (1)wherein R represents at least one of alkaline earth metals andrare-earth elements excluding Ce; a represents an atomic ratio of Cesatisfying the following relation: 0.1≦a≦0.65; b represents an atomicratio of R satisfying the following relation: 0≦b≦0.55; [1−(a+b)]represents an atomic ratio of Zr satisfying the following relation:0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect.

Examples of the alkaline earth metals represented by R include Be, Mg,Ca, Sr, Ba, and Ra, of which Mg, Ca, Sr, and Ba are preferred. Therare-earth elements represented by R are rare-earth elements excludingCe, and examples thereof include Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu. Among them, Sc, Y, La, Pr, and Nd arepreferred. These alkaline earth metals and rare-earth elements can beused alone or in combination.

The atomic ratio of Ce represented by a ranges from 0.1 to 0.65. If theatomic ratio is less than 0.1, the crystal phase may become unstable todecompose in oxidative-reducing atmospheres at high temperatures therebyto decrease the catalytic performance. If it exceeds 0.65, the catalystmay have a decreased specific surface area thereby to fail to exhibitsatisfactory catalytic performance. The atomic ratio of R represented byb ranges from 0 to 0.55. Namely, R is not an essential component but isan optional component to be contained optionally. The atomic ratiothereof is, if contained, 0.55 or less. An atomic ratio of R exceeding0.55 may invite phase separation or formation of other composite oxidephases.

The atomic ratio of Zr represented by [1-(a+b)] ranges from 0.35 to 0.9.The atomic ratio of Zr is preferably ranges from 0.5 to 0.9 and morepreferably ranges from 0.6 to 0.9.

The zirconia composite oxide represented by the general formula (1)preferably has an atomic ratio of Ce of 0.5 or less. When the exhaustgas purifying catalyst comprises the zirconia composite oxiderepresented by the general formula (1) in combination with the ceriacomposite oxide represented by the general formula (2) mentioned below,the atomic ratio of Zr in the zirconia composite oxide represented bythe general formula (1) is preferably greater than the atomic ratio ofZr in the ceria composite oxide represented by the general formula (2).

The amount c represents an oxygen defect which in turn means a ratio ofvacancies formed in a fluorite-like crystal lattice generally composedof oxides of Zr, Ce, and R.

These zirconia composite oxides can be prepared according to any ofknown processes without being limited to a particular process.

The zirconia composite oxides can be prepared, for example, by addingwater to a zirconium oxide powder and/or a zirconia hydroxide powder toobtain a slurry, adding an aqueous solution containing a cerium salt, analkaline earth metal salt and/or a rare-earth element excluding Ce(hereinafter briefly referred to as “rare-earth element”) salt in apredetermined stoichiometric ratio to the slurry, stirring themsufficiently and heat-treating the resulting mixture.

Commercially available zirconium oxide powders and/or zirconia hydroxidepowders can be used herein. Those each having a large specific surfacearea are preferred. The slurry is prepared by adding about 10 parts toabout 50 parts by weight of water to 1 part by weight of the zirconiumoxide powder and/or the zirconia hydroxide powder.

Examples of the salts as the cerium salt, alkaline earth metal saltand/or rare-earth element salt include inorganic salts such as sulfates,nitrate, hydrochlorides and phosphates; and organic salts such asacetates and oxalates, of which nitrates are preferred. These zirconiumsalt, alkaline earth metal salt and/or rare-earth element salt isdissolved in water to obtain an aqueous mixed solution. The ratio ofwater is 0.1 to 10 by weight to 1 part by weight of the salt in suchproportions within the predetermined atomic ratio as to establish astoichiometric ratio.

The aqueous mixed solution is then added to the slurry, the mixture isfully stirred and then heat-treated. The heat treatment is carried outin the following manner. The mixture is initially subjected to dryingunder reduced pressure typically using a vacuum drying apparatus and isthen further dried preferably at 50° C. to 200° C. for 1 to 48 hours toobtain a dried product. The resulting dried product is baked at 400° C.to 1000° C., and preferably at 650° C. to 1000° C. for 1 to 12 hours,and preferably 2 to 4 hours.

The baking procedure is preferably carried out so that at least part ofthe zirconia composite oxide constitutes a solid-solution, for higherthermostability of the zirconia composite oxide. The suitable bakingrelations for forming the solid-solution are appropriately set dependingon the composition and proportion of the zirconia composite oxide.

Alternatively, the zirconia composite oxide may be prepared in thefollowing manner. Initially, a salt solution containing zirconium,cerium, the alkaline earth metal, and/or the rare-earth element isprepared so as to establish a predetermined stoichiometric ratio. Thesolution is added to an alkaline aqueous solution or an aqueous solutionof an organic acid thereby to coprecipitate a salt containing zirconium,cerium, the alkaline earth metal and/or the rare-earth element, and thecoprecipitate is heat-treated.

In this case, water-soluble zirconium oxychloride (zirconyl oxychloride)is preferably used as the zirconium salt. Examples of the salts as thecerium salt, alkaline earth metal salt, and/or rare-earth element saltinclude inorganic salts such as sulfates, nitrates, hydrochlorides, andphosphates; and organic salts such as acetates and oxalates, of whichnitrates are preferred. Examples of the alkaline aqueous solutioninclude aqueous solutions of salts of alkaline metals such as sodium andpotassium; aqueous solutions of such as ammonia and ammonium carbonate;and any suitable buffers. The alkaline aqueous solution is prepared, ifused, so that the solution after addition of the alkaline aqueoussolution has a pH of about 8 to 11. Examples of the aqueous solution ofan organic acid include aqueous solutions of oxalic acid or citric acid.

The heat treatment can be carried out by the above-mentioned procedureafter filtrating and rinsing the coprecipitate.

The zirconia composite oxide may also be prepared in the followingmanner. Initially, a mixed alkoxide solution containing zirconium,cerium, the alkaline earth metal, and/or the rare-earth element isprepared so as to establish a predetermined stoichiometric ratio. Themixed alkoxide solution is coprecipitated or hydrolyzed by adding thesame to deionized water, and the resulting coprecipitate or hydrolysateis heat-treated.

In this case, the mixed alkoxide solution may be prepared by mixingalkoxides of zirconium, cerium, the alkaline earth metal and/or therare-earth element alkoxide in an organic solvent. Examples of alkoxymoieties constituting the respective alkoxides include alkoxy such asmethoxy, ethoxy, propoxy, isopropoxy and butoxy; and alkoxyalcholatessuch as methoxyethylate, methoxypropylate, methoxybutylate,ethoxyethylate, ethoxypropylate, propoxyethylate and butoxyethylate.

Examples of the organic solvent include aromatic hydrocarbons, aliphatichydrocarbons, alcohols, ketones and esters, of which aromatichydrocarbons such as benzene, toluene and xylenes are preferred.

The heat treatment can be carried out by the above-mentioned procedureafter filtrating and rinsing the coprecipitate or hydrolysate.

The ceria composite oxides are represented by the following generalformula (2):Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (2)wherein L represents at least one of alkaline earth metals andrare-earth elements excluding Ce; d represents an atomic ratio of Zrsatisfying the following relation: 0.2≦d≦0.7; e represents an atomicratio of L satisfying the following relation: 0≦e≦0.2; [1−(d+e)]represents an atomic ratio of Ce satisfying the following relation:0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.

The same as the alkaline earth metals and rare-earth elementsrepresented by R can be used as the alkaline earth metals and/orrare-earth elements represented by L. Preferred examples of the alkalineearth metals include Mg, Ca, Sr, and Ba, and preferred examples of therare-earth elements include Sc, Y, La, Pr, and Nd. These alkaline earthmetals and rare-earth elements can be used alone or in combination.

The atomic ratio of Zr represented by d ranges from 0.2 to 0.7. If theatomic ratio is less than 0.2, the resulting catalyst may have adecreased specific surface area thereby to fail to exhibit sufficientcatalytic performance. If it exceeds 0.7, the catalyst may havedecreased oxygen occlusion capability to fail to exhibit sufficientcatalytic performance. The atomic ratio of L represented by e rangesfrom 0 to 0.2. Namely, L is not an essential component but an optionalcomponent to be contained optionally in an atomic ratio of, ifcontained, 0.2 or less. An atomic ratio of L exceeding 0.2 may invitephase separation or formation of other composite oxide phases.

The atomic ratio of Ce represented by [1-(d+e)] ranges from 0.3 to 0.8,and preferably ranges from 0.4 to 0.6.

The ceria composite oxides represented by the general formula (2) eachpreferably have an atomic ratio of Zr of 0.5 or less. When used incombination with the zirconia composite oxide represented by the generalformula (1) in the exhaust gas purifying catalyst, the atomic ratio ofCe in the ceria composite oxide represented by the general formula (2)is preferably greater than the atomic ratio of Ce in the zirconiacomposite oxide represented by the general formula (1).

The amount f represents an oxygen defect which in turn means a ratio ofvacancies formed in a fluorite-like crystal lattice generally composedof oxides of Ce, Zr, and L.

These ceria composite oxides can be prepared by the same procedures asin the production of the zirconia composite oxides.

When the zirconia composite oxide or the ceria composite oxide actuallyused has an atomic ratio falling both within the atomic ratios of therespective elements of the zirconia composite oxides represented by thegeneral formula (1) and within the atomic ratios of the respectiveelements of the ceria composite oxides represented by the generalformula (2), it can be classified as any of these composite oxideswithout being limited to a particular category. The category, forexample, is appropriately set according to the formulation to beincorporated (to be supported or mixed) when a plurality of the zirconiacomposite oxides and/or the ceria composite oxides are used. When thenoble metals are supported, for example, the ceria composite oxide canbe distinguished from the zirconia composite oxide by allowing the ceriacomposite oxide to support not Rh but Pt alone.

The same as listed above can be used as the theta-alumina herein.

Likewise, the same as listed above can be used as the alpha-aluminaherein.

The gamma-alumina includes, but is not specifically limited to, knowngamma-alumina used as an exhaust gas purifying catalyst.

The theta-alumina and/or alpha-alumina to be mixed in these supportingembodiments may comprise La and/or Ba, as is described above. Namely,one represented by the following general formula (7) is preferably used:(Al_(1−g)D_(g))₂O₃  (7)wherein D represents La and/or Ba; and g represents an atomic ratio of Dsatisfying the following relation: 0≦g≦0.5.

D represents La and/or Ba, and the atomic ratio of D represented by granges from 0 to 0.5. Namely, La and/or Ba is not an essential componentbut an optional component to be contained optionally in an atomic ratioof, if contained, 0.5 or less.

SrZrO₃ can be prepared, for example, by the procedure of the productionmethod of the zirconia composite oxides using a zirconium salt and astrontium salt, or an alkoxide of zirconium and an alkoxide ofstrontium.

LaAlO₃ can be prepared, for example, by the procedure of the productionmethod of the zirconia composite oxides using a lanthanum salt and analuminum salt, or an alkoxide of lanthanum and an alkoxide of aluminum.

The amount of the thermostable oxides is not specifically limited andis, for example, such that the total amount of the thermostable oxidesfalls within a range of 0.5 parts to 30 parts by weight, and preferably0.5 parts to 10 parts by weight, to 1 part by weight of at least one oftheta-alumina and alpha-alumina which supports the perovskite-typecomposite oxide containing a noble metal. If the amount of thethermostable oxides is less than the above-specified range, the catalystmay not have sufficiently improved thermostability. If it is more thanthe above-specified range, the catalyst may comprise an excess amount ofthermostable oxides, which may invite disadvantages in cost andproduction.

The mixing procedure of the thermostable oxides is not specificallylimited, as long as it can physically mix the thermostable oxides withat least one of theta-alumina and alpha-alumina supporting theperovskite-type composite oxide. For example, a powder of at least oneof theta-alumina and alpha-alumina supporting the perovskite-typecomposite oxide containing a noble metal may be mixed with a powder ofthe thermostable oxides by dry-mixing or wet-mixing.

The thermostable oxide preferably comprises a thermostable oxidesupporting a noble metal. By incorporating the thermostable oxidesupporting a noble metal, the resulting catalyst can have a furtherincreased catalytic activity and further improved catalytic performance,in addition to the action of the noble metal contained in theperovskite-type composite oxide containing a noble metal.

Examples of the noble metal herein include Pd, Rh, and Pt, of which Rhand Pt are preferred. These noble metals can be used alone or incombination.

The noble metal can be supported by the thermostable oxide according toa known procedure not specifically limited. It can be supported, forexample, by preparing a salt-containing solution comprising the noblemetal, impregnating the thermostable oxide with the salt-containingsolution and baking the resulting article.

The same as listed above can be used as the salt-containing solution.Practical examples thereof include aqueous nitrate solution,dinitrodiammine nitrate solution, and aqueous chloride solution. Morespecifically, examples of the palladium salt solution include aqueouspalladium nitrate solution, dinitrodiammine palladium nitrate solution,and palladium tetraammine nitrate solution. Examples of the rhodium saltsolution include rhodium nitrate solution and rhodium chloride solution.Examples of the platinum salt solution include dinitrodiammine platinumnitrate solution, chloroplatinic acid solution, and platinum tetraamminesolution.

After impregnating the thermostable oxide with the noble metal, theresulting article is dried, for example, at 50° C. to 200° C. for 1 to48 hours and is baked at 350° C. to 1000° C. for 1 to 12 hours.

Alternatively, the noble metal can be supported by the thermostableoxide, for example, in the following manner. When the thermostable oxideis the zirconia composite oxide or the ceria composite oxide, the noblemetal is coprecipitated with the respective components of the zirconiacomposite oxide or the ceria composite oxide by adding a solution of thenoble metal salt during coprecipitation or hydrolysis of the saltsolution or mixed alkoxide solution containing zirconium, cerium, andthe alkaline earth metal and/or the rare-earth element, and thecoprecipitate is then baked.

Another example of a method for allowing the thermostable oxide tosupport the noble metal is as follows. When the thermostable oxide isone of the theta-alumina, alpha-alumina, and gamma-alumina, the noblemetal is coprecipitated with the theta-alumina, alpha-alumina, orgamma-alumina by adding a solution of the noble metal salt duringprecipitation of the theta-alumina, alpha-alumina, or gamma-alumina froman aqueous aluminum salt solution typically using ammonia in itsproduction process, and the coprecipitate is baked.

When two or more different noble metals are supported, these noblemetals may be supported simultaneously in one step or sequentially inplural steps.

The amount of the noble metals is set according to the purpose and theuse thereof and is, for example, 0.01% to 3.0% by weight, and preferably0.05% to 1.0% by weight of the total amount of the thermostable oxides.

Examples of the thermostable oxide supporting a noble metal thusprepared include a zirconia composite oxide supporting a noble metal, aceria composite oxide supporting a noble metal, a theta-aluminasupporting a noble metal, and a gamma-alumina supporting a noble metal.

The zirconia composite oxide supporting a noble metal is preferably azirconia composite oxide supporting Pt and/or Rh. In this case, theamount of Pt and/or Rh is 0.01% to 2.0% by weight, and preferably 0.05%to 1.0% by weight of the amount of the zirconia composite oxide.

The ceria composite oxide supporting a noble metal is preferably a ceriacomposite oxide supporting Pt. In this case, the amount of Pt is 0.01%to 2.0% by weight, and preferably 0.05% to 1.0% by weight of the amountof the ceria composite oxide.

The theta-alumina supporting a noble metal is preferably a theta-aluminasupporting Pt and/or Rh. In this case, the amount of Pt and/or Rh is0.01% to 2.0% by weight, and preferably 0.05% to 1.0% by weight of theamount of the theta-alumina.

The gamma-alumina supporting a noble metal is preferably a gamma-aluminasupporting Pt and/or Rh. In this case, the amount of Pt and/or Rh is0.01% to 2.0% by weight, and preferably 0.05% to 1.0% by weight of theamount of the gamma-alumina.

Of these thermostable oxides each supporting a noble metal, the ceriacomposite oxide supporting a noble metal is preferred. The use of theceria composite oxide supporting a noble metal can improve the oxygenstorage performance.

The entire thermostable oxide may support the noble metal.Alternatively, the thermostable oxide may comprise both a thermostableoxide supporting the noble metal and a thermostable oxide not supportingthe noble metal.

In an embodiment in which the perovskite-type composite oxide containinga noble metal is mixed at least one of theta-alumina and alpha-alumina(hereinafter referred to as “mixing embodiment”), the amount of at leastone of theta-alumina and alpha-alumina with respect to theperovskite-type composite oxide containing a noble metal is notspecifically limited and is, for example, 0.5 parts to 20 parts byweight, and preferably 0.5 parts to 10 parts by weight to 1 part byweight of the perovskite-type composite oxide containing a noble metal.An amount of at least one of theta-alumina and alpha-alumina less thanthe above-specified range may invite insufficient dispersion of theperovskite-type composite oxide containing a noble metal and may fail toprevent grain growth in an atmosphere of high temperature. An amount ofat least one of theta-alumina and alpha-alumina exceeding theabove-specified range may invite disadvantages in cost and production.

The mixing procedure of the perovskite-type composite oxide containing anoble metal with at least one of theta-alumina and alpha-alumina is notspecifically limited, as long as it can physically mix theperovskite-type composite oxide containing a noble metal with at leastone of theta-alumina and alpha-alumina. For example, a powder of theperovskite-type composite oxide containing a noble metal is mixed with apowder of at least one of theta-alumina and alpha-alumina by dry-mixingor wet-mixing.

The exhaust gas purifying catalyst of the present invention according tothe mixing embodiment may further be mixed with at least onethermostable oxide selected from the group consisting of zirconiacomposite oxides (the zirconia composite oxides represented by thegeneral formula (1)), ceria composite oxides (the ceria composite oxidesrepresented by the general formula (2)), gamma-alumina, SrZrO₃ andLaAlO₃. By mixing these thermostable oxides, the perovskite-typecomposite oxide containing a noble metal can exhibit further improvedthermostability. This easily enables the exhaust gas purifying catalystof the present invention to be used in a very severe atmosphere of hightemperature such as in manifold converters.

The same as listed above can be used as the zirconia composite oxides(the zirconia composite oxides represented by the general formula (1)),the ceria composite oxides (the ceria composite oxides represented bythe general formula (2)), gamma-alumina, SrZrO₃ and LaAlO₃ herein.

The mixing ratio of these thermostable oxides (excluding thetheta-alumina and alpha-alumina; this is to be repeated in thefollowing) is not specifically limited and is, for example, such thatthe total amount of the thermostable oxides excluding the theta-aluminaand alpha-alumina is 0.5 parts to 30 parts by weight, and preferably 0.5parts to 10 parts by weight to 1 part by weight of the perovskite-typecomposite oxide containing a noble metal. If the amount of thethermostable oxides is less than the above-specified range, thethermostability may not be sufficiently improved. If it exceeds theabove-specified range, the resulting catalyst may contain excess amountsof the thermostable oxides, which may invite disadvantages in cost andproduction.

The mixing procedure of the thermostable oxide is not specificallylimited, as long as it can physically mix the thermostable oxides withthe perovskite-type composite oxide containing a noble metal togetherwith at least one of theta-alumina and alpha-alumina. For example, apowder of at least one of theta-alumina and alpha-alumina and a powderof the thermostable oxides are mixed with the perovskite-type compositeoxide containing a noble metal by dry-mixing or wet-mixing.

The thermostable oxide preferably comprises the thermostable oxidesupporting a noble metal, as described above. By incorporating thethermostable oxide supporting a noble metal, the resulting catalyst canexhibit further increased catalytic activity and further improvedcatalytic performance, in addition to the action of the noble metalcontained in the perovskite-type composite oxide containing a noblemetal.

Examples of the noble metal herein include Pd, Rh and Pt, of which Rhand Pt are preferred. These noble metals can be used alone or incombination. The amount of the noble metal is, for example, 0.01% to3.0% by weight, and preferably 0.05% to 1.0% by weight of the totalamount of the thermostable oxides, as described above.

Examples of the thermostable oxide supporting a noble metal includezirconia composite oxides each supporting a noble metal (preferably theabove-mentioned zirconia composite oxide supporting Pt and/or Rh), ceriacomposite oxides each supporting a noble metal (preferably theabove-mentioned ceria composite oxide supporting Pt), theta-aluminasupporting a noble metal (preferably the above-mentioned theta-aluminasupporting Pt and/or Rh), and gamma-alumina supporting a noble metal(preferably the above-mentioned gamma-alumina supporting Pt and/or Rh).

In the exhaust gas purifying catalyst of the present invention accordingto the mixing embodiment, the perovskite-type composite oxide containinga noble metal may be supported not by the theta-alumina and/oralpha-alumina but by any of other thermostable oxides (preferably,zirconia composite oxides (the zirconia composite oxides represented bythe general formula (1)), ceria composite oxides (the ceria compositeoxides represented by the general formula (2)), SrZrO₃ and LaAlO₃) andthen mixed with at least one of the theta-alumina and alpha-alumina.

The perovskite-type composite oxide containing a noble metal can besupported by the procedure in the supporting of the perovskite-typecomposite oxide containing a noble metal by at least one oftheta-alumina and alpha-alumina. Specifically, the supporting procedurecan be carried out by incorporating the thermostable oxide into apre-crystallization composition before the crystallization of theperovskite-type composite oxide containing a noble metal andheat-treating the resulting mixture in the course of production of theperovskite-type composite oxide containing a noble metal.

More specifically, the supporting can be carried out by mixing a powderof the thermostable oxide typically with a mixed solution(pre-crystallization composition) of elementary components constitutingthe perovskite-type composite oxide containing a noble metal or with theresulting precipitate (pre-crystallization composition), andheat-treating the resulting mixture.

When the perovskite-type composite oxide comprising a noble metal as aconstituent is prepared by the coprecipitation process, for example, thepowder of the thermostable oxide is added typically to the preparedaqueous mixed salt solution (pre-crystallization composition), theresulting coprecipitate (pre-crystallization composition) or a driedproduct thereof (pre-crystallization composition), and the resultingmixture is then heat-treated.

When the perovskite-type composite oxide comprising a noble metal as aconstituent is prepared by the citrate complex process, for example, thepowder of the thermostable oxide is added typically to the preparedaqueous citrate mixed salt solution (pre-crystallization composition),the resulting citrate complex (pre-crystallization composition), or aprovisionally baked product thereof (pre-crystallization composition),and the resulting mixture is then heat-treated.

When the perovskite-type composite oxide comprising a noble metal as aconstituent is prepared by the alkoxide process, the powder of thethermostable oxide is added typically to the prepared mixed alkoxidesolution (pre-crystallization composition) or homogenous mixed solution(pre-crystallization composition), the resulting precipitate(pre-crystallization composition), or a dried product thereof(pre-crystallization composition), and the resulting mixture is thenheat-treated.

Among the above-mentioned methods, preferred is the method in which thepowder of the thermostable oxide is added during the course of theproduction of the perovskite-type composite oxide comprising a noblemetal as a constituent and the mixture is heat-treated.

When the perovskite-type composite oxide containing a noble metal issupported by the thermostable oxide and is then mixed with at least oneof theta-alumina and alpha-alumina, the amount of at least one oftheta-alumina and alpha-alumina with respect to the thermostable oxidesupporting the perovskite-type composite oxide containing a noble metalis not specifically limited and is, for example, 0.5 parts to 30 partsby weight, and preferably 0.5 parts to 10 parts by weight to 1 part byweight of the thermostable oxide supporting the perovskite-typecomposite oxide containing a noble metal. If the amount of at least oneof theta-alumina and alpha-alumina is less than the above-specifiedrange, the resulting catalyst may not satisfactorily maintain as acoating layer on a catalyst carrier mentioned later. In contrast, anamount of at least one of theta-alumina and alpha-alumina exceeding theabove-specified range may invite disadvantages in cost and production.

When the perovskite-type composite oxide containing a noble metal issupported by the thermostable oxide and is then mixed with at least oneof theta-alumina and alpha-alumina, the resulting article can also bemixed with the same or another thermostable oxide (preferably, any ofthe zirconia composite oxides, the ceria composite oxides, SrZrO₃ andLaAlO₃) in the above-mentioned proportions by the above-describedprocedure.

The exhaust gas purifying catalyst of the present invention canconstitute, for example, a coating layer on a catalyst carrier. Thecatalyst carrier can be any of known catalyst carriers such as honeycombmonolith carriers derived from cordierite, without being limited to aparticular catalyst carrier.

The coating layer can be formed on the catalyst carrier, for example, inthe following manner. Initially, water is added to the perovskite-typecomposite oxide containing a noble metal and at least one oftheta-alumina and alpha-alumina (any of the supporting embodiments andthe mixing embodiments will do) as well as the thermostable oxide addedaccording to necessity to obtain a slurry. The optionally addedthermostable oxide is at least one thermostable oxide selected from thezirconia composite oxides, the ceria composite oxides, theta-alumina,alpha-alumina, gamma-alumina, SrZrO₃ and LaAlO₃ in the supportingembodiments and is at least one thermostable oxide selected from thezirconia composite oxides, the ceria composite oxides, gamma-alumina,SrZrO₃ and LaAlO₃ in the mixing embodiments (this is to be repeated inthe following). The slurry is then applied to the catalyst carrier, isdried at 50° C. to 200° C. for 1 to 48 hours and is baked at 350° C. to1000° C. for 1 to 12 hours. Alternatively, the coating layer can beformed by adding water to each of the respective components to obtainslurries, mixing these slurries, applying the resulting slurry mixtureto the catalyst carrier, drying at 50° C. to 200° C. for 1 to 48 hoursand then baking at 350° C. to 1000° C. for 1 to 12 hours.

The exhaust gas purifying catalyst of the present invention can also bearranged as a multilayer coating layer on the catalyst carrier. Themultilayer coating layer comprises an outer layer constituting itssurface and an inner layer arranged inside the outer layer.

When the coating layer comprises multiple layers, the perovskite-typecomposite oxide containing a noble metal and at least one oftheta-alumina and alpha-alumina may be contained in different layers butare preferably contained in the same layer(s). These components may becontained in two or more layers, as long as they are contained in thesame layer(s). The layer(s) which will contain these components areappropriately decided depending on the purpose and the use of thecatalyst.

The inner layer can be prepared by applying the slurry containing therespective components to the catalyst carrier, drying and baking theresulting article, as described above. The outer layer can be preparedby applying the slurry containing the respective components to the innerlayer formed on the catalyst carrier, drying and baking the resultingarticle, as described above.

When the exhaust gas purifying catalyst of the present inventioncomprises multiple layers, it is preferred that the inner layercomprises the theta-alumina and/or theta-alumina supporting theperovskite-type composite oxide containing a noble metal, and/or, thethermostable oxide supporting the perovskite-type composite oxidecontaining a noble metal.

By incorporating at least one of theta-alumina and alpha-aluminasupporting the perovskite-type composite oxide containing a noble metal,and/or, the thermostable oxide supporting the perovskite-type compositeoxide containing a noble metal into the inner layer, the catalyst can beprevented from poisoning and thermal degradation and can exhibit furtherimproved catalytic performance.

When the exhaust gas purifying catalyst of the present inventioncomprises the multiple layers as above, each of the perovskite-typecomposite oxides each containing a noble metal can be used alone or incombination. Specifically, for example, the perovskite-type compositeoxide containing a noble metal can be contained in the inner layer aloneor the outer layer alone. In addition, perovskite-type composite oxideseach containing the same or different types of plural noble metals maybe contained in either one of the inner layer and outer layer or in bothof the inner layer and outer layer.

When the exhaust gas purifying catalyst of the present inventioncomprises the multiple layers, the Pd containing perovskite-typecomposite oxide is preferably contained in the inner layer. Byincorporating the Pd containing perovskite-type composite oxide into theinner layer, the poisoning and thermal degradation of Pd contained inthe perovskite-type composite oxide can be prevented thereby to improvethe durability.

When the exhaust gas purifying catalyst of the present inventioncomprises the multiple layers, the Rh-containing perovskite-typecomposite oxide is preferably contained in the outer layer. Byincorporating the Rh-containing perovskite-type composite oxide into theouter layer, alloying with Pd can be prevented typically in the casewhere the Pd containing perovskite-type composite oxide is contained inthe inner layer.

When the exhaust gas purifying catalyst of the present inventioncomprises the multiple layers, the Pt containing perovskite-typecomposite oxide is preferably contained in the inner layer and/or theouter layer.

When the exhaust gas purifying catalyst of the present inventioncomprises the multiple layers, it is preferred that the noble metalcontained in the outer layer (including the noble metal contained in theperovskite-type composite oxide, and the noble metal supported by thethermostable oxide) is Rh and/or Pt and that the noble metal containedin the inner layer (including the noble metal contained in theperovskite-type composite oxide, and the noble metal supported by thethermostable oxide) is at least Pd. This configuration can prevent thepoisoning and thermal degradation of the catalyst by incorporating Pdinto the inner layer and can further improve the catalytic performanceby the action of Rh and/or Pt contained in the outer layer.

When the exhaust gas purifying catalyst of the present inventioncomprises the multiple layers, it is preferred that the ceria compositeoxide and/or theta-alumina each supporting a noble metal is contained inthe inner layer, and that at least two different thermostable oxidesselected from the zirconium composite oxide supporting a noble metal,the ceria composite oxide supporting a noble metal, the theta-aluminasupporting a noble metal, and the gamma-alumina supporting a noble metalare contained in the outer layer.

More specifically, it is preferred that the inner layer comprises thetheta-alumina and the ceria composite oxide supporting Pt and that theouter layer comprises at least one thermostable oxide selected from thegroup consisting of the zirconia composite oxide supporting Pt and Rh,the ceria composite oxide supporting Pt, and the theta-aluminasupporting Pt and Rh.

The exhaust gas purifying catalyst of the present invention may furthercomprise any of sulfates, carbonates, nitrates, and acetates of Ba, Ca,Sr, Mg, and La. Any of these sulfates, carbonates, nitrates, andacetates is preferably contained in a layer containing Pd, when thecatalyst comprises the multiple layers. By incorporating any of thesulfates, carbonates, nitrates, and acetates, the poisoning of Pdtypically by the action of hydrocarbons (HC) can be prevented thereby toavoid decrease in catalytic activity. Of these salts, BaSO₄ ispreferably used.

The amount of any of these sulfates, carbonates, nitrates, and acetatesmay be appropriately set depending on the purpose and the use thereof.The sulfate, carbonate, nitrate and/or acetate can be incorporated intothe inner layer and/or the outer layer, for example, by adding thesulfate, carbonate, nitrate, and/or acetate into the slurry for formingthe inner layer and/or the outer layer.

The inner layer may comprise multiple layers, according to the purposeand the use thereof. The same procedure as above can be applied to formthe inner layer as multiple layers.

The exhaust gas purifying catalyst of the present invention thusobtained can allow a noble metal to be stably contained in aperovskite-type composite oxide and, in addition, remarkably increasethe thermostability of the perovskite-type composite oxide by the actionof at least one of theta-alumina and alpha-alumina.

In each perovskite-type composite oxide, the noble metal is finely andhighly dispersed thereby to maintain its high catalytic activity even inlong-term use in an atmosphere of high temperature. This is because ofthe self-regenerative function in which the noble metal repetitivelyundergoes solid-solution under an oxidative atmosphere and depositionunder a reducing atmosphere with respect to the perovskite structure.This self-regenerative function also enables the resulting catalyst toachieve satisfactory catalytic activity even if the amount of the noblemetal is significantly reduced.

The perovskite-type composite oxide containing a noble metal exhibitsincreased thermostability by the action of at least one of theta-aluminaand alpha-alumina. This prevents the perovskite-type composite oxidefrom grain growth and a decreased specific surface area in an atmosphereof high temperature of, for example, 900° C. to 1000° C., or furtherexceeding 1050° C.

Thus, the exhaust gas purifying catalyst of the present invention canmaintain the catalytic activity of the noble metal at a high level overa long time and achieve satisfactory exhaust gas purifying performance,even in an atmosphere of high temperature exceeding 900° C. to 1000° C.It can be advantageously used as an automobile exhaust gas purifyingcatalyst.

EXAMPLES

The present invention will be illustrated in further detail withreference to several examples and comparative examples below, which arenever intended to limit the scope of the invention.

(1) Production of Zirconia Composite Oxide Production Example A1Zirconium oxychloride 26.6 g (0.079 mol)  (corresponding to 36.56% bymass of ZrO₂, the same is true hereinafter) Cerium nitrate 6.9 g (0.016mol) Lanthanum nitrate 0.4 g (0.001 mol) Neodymium nitrate 1.8 g (0.004mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A1) comprising aZr_(0.79)Ce_(0.16)La_(0.01)Nd_(0.04) oxide, in which cerium andlanthanum constitute a solid solution.

The powdery zirconia composite oxide was impregnated with a rhodiumnitrate solution, dried at 100° C. and baked at 500° C. to obtain apowdery Rh supporting zirconia composite oxide (Production Example A1-1)supporting 0.5% by weight of Rh. The powdery zirconia composite oxidewas impregnated with a dinitrodiammine platinum nitrate solution, driedat 100° C., impregnated with a rhodium nitrate solution, dried at 100°C. and baked at 500° C. to obtain a powdery Pt—Rh supporting zirconiacomposite oxide (Production Example A1-2) supporting 0.15% by weight ofPt and 0.15% by weight of Rh. Production Example A2 Zirconiumoxychloride 20.2 g (0.060 mol) Cerium nitrate 13.0 g (0.030 mol)Lanthanum nitrate  2.2 g (0.005 mol) Yttrium nitrate  1.9 g (0.005 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A2) comprising a Zr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05)oxide in which cerium and lanthanum constitute a solid solution.Production Example A3 Zirconium oxychloride 16.9 g (0.050 mol) Ceriumnitrate 17.4 g (0.040 mol) Lanthanum nitrate  2.2 g (0.005 mol)Neodymium nitrate  2.2 g (0.005 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A3) comprising aZr_(0.50)Ce_(0.40)La_(0.05)Nd_(0.05) oxide, in which cerium andlanthanum constitute a solid solution.

The powdery zirconia composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., impregnatedwith a rhodium nitrate solution, dried at 100° C. and baked at 500° C.to obtain a powdery Pt—Rh supporting zirconia composite oxide(Production Example A3-1) supporting 0.27% by weight of Pt and 1.33% byweight of Rh. Production Example A4 Zirconium oxychloride 21.9 g (0.065mol) Cerium nitrate 13.0 g (0.030 mol) Lanthanum nitrate  0.9 g (0.002mol) Yttrium nitrate  1.1 g (0.003 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A4) comprising a Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03)oxide in which cerium and lanthanum constitute a solid solution.Production Example A5 Zirconium oxychloride 23.6 g (0.070 mol)  Ceriumnitrate 8.1 g (0.020 mol) Lanthanum nitrate 2.2 g (0.005 mol) Yttriumnitrate 1.9 g (0.005 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A5) comprising a Zr_(0.70)Ce_(0.20)La_(0.05)Y_(0.05)oxide in which cerium and lanthanum constitute a solid solution.Production Example A6 Zirconium oxychloride 25.6 g (0.076 mol)  Ceriumnitrate 7.8 g (0.018 mol) Lanthanum nitrate 1.7 g (0.002 mol) Neodymiumnitrate 1.8 g (0.004 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A6) comprising aZr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide, in which cerium andlanthanum constitute a solid solution.

The powdery zirconia composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., impregnatedwith a rhodium nitrate solution, dried at 100° C. and baked at 500° C.to obtain a powdery Pt—Rh supporting zirconia composite oxide(Production Example A6-1) supporting 0.20% by weight of Pt and 0.30% byweight of Rh; a powdery Pt—Rh supporting zirconia composite oxide(Production Example A6-2) supporting 1.00% by weight of Pt and 1.00% byweight of Rh; a powdery Pt—Rh supporting zirconia composite oxide(Production Example A6-3) supporting 0.30% by weight of Pt and 1.40% byweight of Rh; or a powdery Pt—Rh supporting zirconia composite oxide(Production Example A6-4) supporting 0.27% by weight of Pt and 1.33% byweight of Rh. Production Example A7 Zirconium oxychloride 20.2 g (0.060mol) Cerium nitrate 13.0 g (0.030 mol) Lanthanum nitrate  2.2 g (0.005mol) Yttrium nitrate  1.9 g (0.005 mol)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery zirconia composite oxide(Production Example A7) comprising a Zr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05)oxide. Production Example A8 Zirconium oxychloride 21.9 g (0.065 mol)Cerium nitrate 13.0 g (0.030 mol) Lanthanum nitrate  0.9 g (0.002 mol)Yttrium nitrate  1.1 g (0.003 mol)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery zirconia composite oxide(Production Example A8) comprising a Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03)oxide. Production Example A9 Zirconium oxychloride 27.0 g (0.080 mol) Cerium nitrate 6.5 g (0.015 mol) Lanthanum nitrate 0.9 g (0.002 mol)Neodymium nitrate 1.3 g (0.003 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A9) comprising aZr_(0.80)Ce_(0.15)La_(0.02)Nd_(0.03) oxide, in which cerium andlanthanum constitute a solid solution.

The powdery zirconia composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., impregnatedwith a rhodium nitrate solution, dried at 100° C. and baked at 500° C.to obtain a powdery Pt—Rh supporting zirconia composite oxide(Production Example A9-1) supporting 0.27% by weight of Pt and 1.33% byweight of Rh. Separately, the powdery zirconia composite oxide wasimpregnated with a rhodium nitrate solution, dried at 100° C. and bakedat 500° C. to obtain a powdery Rh supporting zirconia composite oxide(Production Example A9-2) supporting 0.83% by weight of Rh. ProductionExample A10 Zirconium oxychloride 16.9 g (0.050 mol) Cerium nitrate 17.4g (0.040 mol) Lanthanum nitrate  2.2 g (0.005 mol) Yttrium nitrate  1.9g (0.005 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A10) comprising aZr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05) oxide, in which cerium and lanthanumconstitute a solid solution. Production Example A11 Zirconiumoxychloride 20.2 g (0.060 mol) Cerium nitrate 13.0 g (0.030 mol)Lanthanum nitrate  2.2 g (0.005 mol) Neodymium nitrate  2.2 g (0.005mol)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery zirconia composite oxide(Production Example A11) comprising aZr_(0.60)Ce_(0.30)La_(0.05)Nd_(0.05) oxide. Production Example A12Zirconium oxychloride 23.6 g (0.070 mol) Cerium nitrate 10.8 g (0.025mol) Lanthanum nitrate  1.7 g (0.002 mol) Neodymium nitrate  1.3 g(0.003 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A12) comprising aZr_(0.70)Ce_(0.25)La_(0.02)Nd_(0.03) oxide, in which cerium andlanthanum constitute a solid solution.

The powdery zirconia composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., impregnatedwith a rhodium nitrate solution, dried at 100° C. and baked at 500° C.to obtain a powdery Pt—Rh supporting zirconia composite oxide(Production Example A12-1) supporting 0.75% by weight of Pt and 1.25% byweight of Rh. Production Example A13 Zirconium oxychloride 23.6 g (0.070mol) Cerium nitrate 10.8 g (0.025 mol) Lanthanum nitrate  1.7 g (0.002mol) Yttrium nitrate  1.1 g (0.003 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A13) comprising Zr_(0.70)Ce_(0.25)La_(0.02)Y_(0.03)oxide, in which cerium and lanthanum constitute a solid solution.Production Example A14 Zirconium ethoxyethylate 31.4 g (0.070 mol)Cerium ethoxyethylate 10.2 g (0.025 mol) Praseodymium ethoxyethylate 0.8 g (0.002 mol) Neodymium ethoxyethylate  1.2 g (0.003 mol)

The above listed components were dissolved in 200 mL of toluene withstirring to obtain a mixed alkoxide solution. The alkoxides werehydrolyzed by adding the mixed alkoxide solution dropwise to 600 mL ofdeionized water over about ten minutes. The toluene and deionized waterwere distilled off from the hydrolyzed solution to dryness to obtain apre-crystallization composition. After being subjected to forced airdrying at 60° C. for twenty four hours, the dried product heat treated(baked) in an electric furnace at 800° C. for one hour to obtain apowdery zirconia composite oxide (Production Example A14) comprising aZr_(0.70)Ce_(0.25)Pr_(0.02)Nd_(0.03) oxide.

(2) Production of Ceria Composite Oxide Production Example B1 Ceriummethoxypropylate 24.4 g (0.060 mol) Zirconium methoxypropylate 13.4 g(0.030 mol) Yttrium methoxypropylate  3.6 g (0.010 mol)

The above listed components were dissolved in 200 mL of toluene withstirring to obtain a mixed alkoxide solution. The alkoxides werehydrolyzed by adding 80 mL of deionized water dropwise to the solution.The toluene and deionized water were distilled off from the hydrolyzedsolution to dryness to obtain a pre-crystallization composition. Afterbeing subjected to forced air drying at 60° C. for twenty four hours,the dried product was baked in an electric furnace at 450° C. for threehours to obtain a powdery ceria composite oxide (Production Example B1)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide.

The powdery ceria composite oxide was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C. and baked at 500° C. toobtain a powdery Pt supporting ceria composite oxide (Production ExampleB1-1) supporting 0.25% by weight of Pt; a powdery Pt supporting ceriacomposite oxide (Production Example B1-2) supporting 0.50% by weight ofPt; a powdery Pt supporting ceria composite oxide (Production ExampleB1-3) supporting 1.00% by weight of Pt; a powdery Pt supporting ceriacomposite oxide (Production Example B1-4) supporting 0.30% by weight ofPt; a powdery Pt supporting ceria composite oxide (Production ExampleB1-5) supporting 0.80% by weight of Pt; a powdery Pt supporting ceriacomposite oxide (Production Example B1-6) supporting 0.10% by weight ofPt; a powdery Pt supporting ceria composite oxide (Production ExampleB1-7) supporting 0.33% by weight of Pt; a powdery Pt supporting ceriacomposite oxide (Production Example B1-8) supporting 0.67% by weight ofPt; a powdery Pt supporting ceria composite oxide (Production ExampleB1-9) supporting 1.38% by weight of Pt; or a powdery Pt supporting ceriacomposite oxide (Production Example B1-10) supporting 1.50% by weight ofPt. Production Example B2 Cerium nitrate 17.4 g (0.040 mol) Zirconiumoxychloride 16.9 g (0.050 mol) Yttrium nitrate  3.8 g (0.010 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery ceria composite oxide(Production Example B2) comprising a Ce_(0.40)Zr_(0.50)Y_(0.10) oxide.

The powdery ceria composite oxide was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C. and baked at 500° C. toobtain a powdery Pt supporting ceria composite oxide (Production ExampleB2-1) supporting 0.20% by weight of Pt. Production Example B3 Ceriumnitrate 26.1 g (0.060 mol) Zirconium oxychloride 20.2 g (0.030 mol)Yttrium nitrate  3.8 g (0.010 mol)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery ceria composite oxide(Production Example B3) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide.

The powdery ceria composite oxide was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C. and baked at 500° C. toobtain a powdery Pt supporting ceria composite oxide (Production ExampleB3-1) supporting 1.33% by weight of Pt; a powdery Pt supporting ceriacomposite oxide (Production Example B3-2) supporting 0.33% by weight ofPt; a powdery Pt supporting ceria composite oxide (Production ExampleB3-3) supporting 0.10% by weight of Pt; or a powdery Pt supporting ceriacomposite oxide (Production Example B3-4) supporting 0.67% by weight ofPt. Production Example B4 Cerium methoxypropylate 32.6 g (0.080 mol)Zirconium methoxypropylate  9.0 g (0.020 mol)

The above listed components were dissolved in 200 mL of toluene withstirring to obtain a mixed alkoxide solution. The alkoxides werehydrolyzed by adding 80 mL of deionized water dropwise to the solution.The toluene and deionized water were distilled off from the hydrolyzedsolution to dryness to obtain a pre-crystallization composition. Afterbeing subjected to forced air drying at 60° C. for twenty four hours,the dried product was baked in an electric furnace at 300° C. for threehours to obtain a powdery ceria composite oxide (Production Example B4)comprising Ce_(0.80)Zr_(0.20)O₂.

The powdery ceria composite oxide was impregnated with a palladiumnitrate solution, dried at 100° C. and baked at 300° C. to obtain apowdery Pd supporting ceria composite oxide (Production Example B4-1)supporting 3.30% by weight of Pd. Production Example B5 Ceriummethoxypropylate 12.2 g (0.030 mol) Zirconium methoxypropylate 31.5 g(0.070 mol)

The above listed components were dissolved in 200 mL of toluene withstirring to obtain a mixed alkoxide solution. The alkoxides werehydrolyzed by adding 80 mL of deionized water dropwise to the solution.The toluene and deionized water were distilled off from the hydrolyzedsolution to dryness to obtain a pre-crystallization composition. Afterbeing subjected to forced air drying at 60° C. for twenty four hours,the dried product was baked in an electric furnace at 300° C. for threehours to obtain a powdery ceria composite oxide (Production Example B5)comprising Ce_(0.30)Zr_(0.70)O₂.

The powdery ceria composite oxide was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C., impregnated with a rhodiumnitrate solution, dried at 100° C. and baked at 500° C. to obtain apowdery Pt—Rh supporting ceria composite oxide (Production Example B5-1)supporting 2.00% by weight of Pt and 1.70% by weight of Rh; or a powderyPt—Rh supporting ceria composite oxide (Production Example B5-2)supporting 2.00% by weight of Pt and 1.00% by weight of Rh.

(3) Production of Theta-Alumina Production Example C2 Aluminummethoxyethylate 60.6 g (0.240 mol)  Lanthanum methoxyethylate 0.55 g(0.0015 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlLa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of AlLa composite oxides. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 1000° C. in the air for four hours to obtain apowdery lanthanum containing theta-alumina (Production Example C2)containing 2.0% by weight of lanthanum in terms of La₂O₃. ProductionExample C3 Aluminum methoxyethylate 59.4 g (0.236 mol) Lanthanummethoxyethylate  1.1 g (0.003 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlLa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of AlLa composite oxides. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 1000° C. in the air for four hours to obtain apowdery lanthanum containing theta-alumina (Production Example C3)containing 4.0% by weight of lanthanum in terms of La₂O₃.

The powdery lanthanum containing theta-alumina was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., impregnatedwith a rhodium nitrate solution, dried at 100° C. and baked at 500° C.to obtain a powdery Pt—Rh supporting theta-alumina (Production ExampleC3-1) supporting 1.00% by weight of Pt and 0.17% by weight of Rh.Production Example C4 Aluminum methoxyethylate 44.6 g (0.177 mol)Lanthanum methoxyethylate  2.2 g (0.006 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlLa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of AlLa composite oxides. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 1000° C. in the air for four hours to obtain apowdery lanthanum containing theta-alumina (Production Example C4)containing 10.0% by weight of lanthanum in terms of La₂O₃. ProductionExample C5 Aluminum methoxyethylate 59.4 g (0.236 mol) Bariummethoxyethylate 0.95 g (0.0033 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlBa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of AlBa composite oxides. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 1000° C. in the air for four hours to obtain apowdery barium containing theta-alumina (Production Example C5)containing 4.0% by weight of barium in terms of BaO.

Production Example C6

A powdery theta-alumina (having a specific surface area of 98.4 m²/g,the same is true hereinafter) was impregnated with dinitrodiammineplatinum nitrate solution, dried at 100° C. and baked at 500° C. toobtain a Pt supporting theta-alumina (Production Example C6) supporting0.31% by weight of Pt.

Production Example C7

The powdery theta-alumina was impregnated with a rhodium nitratesolution, dried at 100° C. and baked at 500° C. to obtain a powdery Rhsupporting theta-alumina (Production Example C7) supporting 0.188% byweight of Rh.

Production Example C8

The powdery theta-alumina was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C., impregnated with a rhodiumnitrate solution, dried at 100° C. and baked at 500° C. to obtain apowdery Pt—Rh supporting theta-alumina (Production Example C8-1)supporting 0.40% by weight of Pt and 0.10% by weight of Rh; a powderyPt—Rh supporting theta-alumina (Production Example C8-2) supporting0.50% by weight of Pt and 0.10% by weight of Rh; a powdery Pt—Rhsupporting theta-alumina (Production Example C8-3) supporting 0.50% byweight of Pt and 0.17% by weight of Rh; a powdery Pt—Rh supportingtheta-alumina (Production Example C8-4) supporting 0.57% by weight of Ptand 0.14% by weight of Rh; a powdery Pt—Rh supporting theta-alumina(Production Example C8-5) supporting 0.43% by weight of Pt and 0.21% byweight of Rh; a powdery Pt—Rh supporting theta-alumina (ProductionExample C8-6) supporting 0.33% by weight of Pt and 1.33% by weight ofRh; or a powdery Pt—Rh supporting theta-alumina (Production ExampleC8-7) supporting 1.50% by weight of Pt and 0.67% by weight of Rh.

Production Example C9

The powdery theta-alumina was impregnated with a palladium nitratesolution, dried at 100° C. and baked at 500° C. to obtain a powdery Pdsupporting theta-alumina (Production Example C9-1) supporting 0.40% byweight of Pd; or a powdery Pd supporting theta-alumina (ProductionExample C9-2) supporting 1.10% by weight of Pd.

(4) Production of Gamma-Alumina Production Example C10 Aluminummethoxyethylate 59.4 g (0.236 mol) Lanthanum methoxyethylate  1.1 g(0.003 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlLa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of AlLa composite oxides. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 850° C. in the air for two hours to obtain a powderylanthanum containing gamma-alumina (Production Example C10) containing4.0% by weight of lanthanum in terms of La₂O₃.

The powdery lanthanum containing gamma-alumina was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., impregnatedwith a rhodium nitrate solution, dried at 100° C. and baked at 500° C.to obtain a powdery Pt—Rh supporting lanthanum containing gamma-alumina(Production Example C10-1) supporting 0.33% by weight of Pt and 0.25% byweight of Rh; or a powdery Pt—Rh supporting lanthanum containinggamma-alumina (Production Example C10-2) supporting 2.00% by weight ofPt and 0.20% by weight of Rh.

Production Example C11

A powdery gamma-alumina (having a specific surface area of 200 m²/g, thesame is true hereinafter) was impregnated with a palladium nitratesolution, dried at 100° C. and baked at 500° C. to obtain a powdery Pdsupporting gamma-alumina (Production Example C11-1) supporting 1.60% byweight of Pd; a powdery Pd supporting gamma-alumina (Production ExampleC11-2) supporting 1.63% by weight of Pd; or a powdery Pd supportinggamma-alumina (Production Example C11-3) supporting 0.44% by weight ofPd.

Production Example C12

A powdery gamma-alumina was impregnated with a rhodium nitrate solution,dried at 100° C. and baked at 500° C. to obtain a powdery Rh supportinggamma-alumina (Production Example C12) supporting 1.58% by weight of Rh.

Production Example C13

A powdery gamma-alumina was impregnated with a dinitrodiammine platinumnitrate solution, dried at 100° C., impregnated with a rhodium nitratesolution, dried at 100° C. and baked at 500° C. to obtain a powderyPt—Rh supporting gamma-alumina (Production Example C13-1) supporting1.00% by weight of Pt and 0.57% by weight of Rh; a powdery Pt—Rhsupporting gamma-alumina (Production Example C13-2) supporting 2.00% byweight of Pt and 0.20% by weight of Rh; or a powdery Pt—Rh supportinggamma-alumina (Production Example C13-3) supporting 0.67% by weight ofPt and 0.42% by weight of Rh.

(5) Production of SrZrO₃ Production Example D1 Zirconium oxychloride33.7 g (0.100 mol) Strontium nitrate 28.4 g (0.100 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then baked at 1200° C. forthree hours and dry-pulverized in an attrition mill for forty eighthours to obtain a powdery SrZrO₃ (Production Example D1).

(6) Production of LaAlO₃ Production Example E1 Lanthanum nitrate 43.3 g(0.100 mol) Aluminum nitrate 37.5 g (0.100 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then calcined at 800° C. forone hour to obtain a powdery LaAlO₃ (Production Example E1).

Example PA-1

1) Production of Palladium Containing Perovskite-Type Composite OxideLanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 18.4 g(0.057 mol) Manganese ethoxyethylate  8.9 g (0.038 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeMnPd containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise in the round bottomedflask. As a result, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a LaFeMnPd composite oxide. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for two hours to obtain a powderyperovskite-type composite oxide comprisingLa_(1.00)Fe_(0.57)Mn_(0.38)Pd_(0.05)O₃.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery perovskite-type composite oxide was addedthe powdery theta-alumina. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 6 mil per400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 150 g of the perovskite-type composite oxide and 50g of theta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The resulting exhaust gas purifying catalystcontained 3.26 g of Pd per one liter of the honeycomb carrier.

Example PA-2

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain theta-aluminacontaining a pre-crystallization composition of a LaFePd composite oxidedispersed therein. Next, the theta-alumina containing thepre-crystallization composition dispersed therein was placed on a petridish, subjected to forced air drying at 60° C. for twenty four hours andheat treated in an electric furnace at 650° C. in the air for one hourto obtain a powdery theta-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to alumina of 3:1.

2) Production of Exhaust Gas Purifying Catalyst

The resulting mixture was mixed with deionized water and then mixed withalumina sol to form a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 6 mil per 400 cells, a diameter of80 mm and a length of 95 mm so as to homogeneously apply 200 g of thetheta-alumina supporting the perovskite-type composite oxide per oneliter of the honeycomb carrier. The resulting article was dried at 100°C. and baked at 500° C. to obtain an exhaust gas purifying catalyst. Theresulting exhaust gas purifying catalyst contained 3.26 g of Pd per oneliter of the honeycomb carrier.

Example PA-3

1) Production of Rhodium Containing Perovskite-Type Composite OxideLanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 18.4 g(0.057 mol) Manganese ethoxyethylate  8.9 g (0.038 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeMnRh containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a LaFeMnRh composite oxide. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for two hours to obtain a powderyperovskite-type composite oxide comprisingLa_(1.00)Fe_(0.57)Mn_(0.38)Rh_(0.05)O₃.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery perovskite-type composite oxide was addedthe powdery theta-alumina. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 6 mil per400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 150 g of the perovskite-type composite oxide and 50g of the theta-alumina per one liter of the honeycomb carrier. Theresulting article was dried at 100° C. and baked at 500° C. to obtain anexhaust gas purifying catalyst. The resulting exhaust gas purifyingcatalyst contained 3.15 g of Rh per one liter of the honeycomb carrier.

Example PA-4

1) Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 32.5 g (0.080 mol)Praseodymium ethoxyethylate  8.2 g (0.020 mol) Iron ethoxyethylate 24.2g (0.075 mol) Titanium ethoxyethylate  8.1 g (0.020 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaPrFeTiRh containing homogeneous mixed solution.

The powdery theta-alumina was dispersed in 200 mL of toluene and theabove prepared homogeneous mixed solution was added, followed bystirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain theta-aluminacontaining a dispersed pre-crystallization composition of a LaPrFeTiRhcomposite oxide. Next, the theta-alumina with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderytheta-alumina supporting aLa_(0.80)Pr_(0.20)Fe_(0.75)Ti_(0.20)Rh_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to theta-alumina of 3:1.

2) Production of Exhaust Gas Purifying Catalyst

The resulting powder was mixed with deionized water and further mixedwith alumina sol to obtain a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 6 mil per 400 cells, adiameter of 80 mm and a length of 95 mm so as to homogeneously apply 200g of the theta-alumina supporting the perovskite-type composite oxideper one liter of the honeycomb carrier. The resulting article was driedat 100° C. and baked at 500° C. to obtain an exhaust gas purifyingcatalyst. The resulting exhaust gas purifying catalyst contained 3.16 gof Rh per one liter of the honeycomb carrier.

Example PA-5

1) Production of Rhodium Containing Perovskite-Type Composite OxideLanthanum nitrate 43.3 g (0.100 mol) Iron nitrate 38.4 g (0.095 mol)Aqueous rhodium nitrate solution 11.5 g (corresponding having a Rhcontent of 4.478% to 0.51 g (0.005 mol) by mass of Rh)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery perovskite-type composite oxidecomprising La_(1.00)Fe_(0.95)Rh_(0.05)O₃.

The powdery perovskite-type composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C. and baked at500° C. to obtain a Pt supporting perovskite-type composite oxide. Theamount of Pt supported by the Pt supporting perovskite-type compositeoxide was 1.00% by mass.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery perovskite-type composite oxide was addedthe powdery theta-alumina. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 6 mil per400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 150 g of the perovskite-type composite oxide and 50g of theta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The exhaust gas purifying catalyst contained 3.15 gof Rh and 1.50 g of Pt per one liter of the honeycomb carrier.

Example PA-6

1) Production of Platinum Containing Perovskite-Type Composite OxideLanthanum nitrate  39.0 g (0.090 mol) Strontium nitrate 2.8 g (0.010mol) Iron nitrate 23.0 g (0.057 mol) Manganese nitrate 10.9 g (0.038mol) Dinitrodiammine platinum nitrate 11.48 g (corresponding solutionhaving a Pt content of 8.50% to 0.975 g (0.005 mol) by mass of Pt)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery perovskite-type composite oxidecomprising La_(0.90)Sr_(0.10)Fe_(0.57)Mn_(0.38)Pt_(0.05)O₃.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of exhaust gas purifying Catalyst

To the above prepared powdery perovskite-type composite oxide was addedthe powdery theta-alumina. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 6 mil per400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 60 g of the perovskite-type composite oxide and 50 gof theta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The resulting exhaust gas purifying catalystcontained 2.39 g of Pt per one liter of the honeycomb carrier.

Example PA-7

1) Supporting of Platinum Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum methoxyethylate 34.6 g (0.095 mol) Aluminummethoxyethylate 21.4 g (0.085 mol) Manganese methoxyethylate  2.0 g(0.010 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.04 g (0.005 mol) of silveracetylacetonate and 1.965 g (0.005 mol) of platinum acetylacetonate weredissolved in 200 mL of toluene, and the resulting solution was added tothe mixed alkoxide solution in the round bottomed flask to obtain aLaAgAlMnPt containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the above prepared homogeneous mixed solution was added, followed bystirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain theta-aluminacontaining a dispersed pre-crystallization composition of a LaAgAlMnPtcomposite oxide. Next, the theta-alumina with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderytheta-alumina supporting aLa_(0.95)Ag_(0.05)Al_(0.85)Mn_(0.10)Pt_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to theta-alumina of 54:50.

2) Production of Exhaust Gas Purifying Catalyst

The resulting powder was mixed with deionized water and further mixedwith alumina sol to obtain a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 6 mil per 400 cells, adiameter of 80 mm and a length of 95 mm so as to homogeneously apply 104g of the theta-alumina supporting the perovskite-type composite oxideper one liter of the honeycomb carrier. The resulting article was driedat 100° C. and baked at 500° C. to obtain an exhaust gas purifyingcatalyst. The resulting exhaust gas purifying catalyst contained 2.41 gof Pt per one liter of the honeycomb carrier.

Example PA-8

1) Production of Platinum Containing Perovskite-Type Composite OxideNeodymium methoxypropylate 32.9 g (0.080 mol) Barium methoxypropylate 3.2 g (0.001 mol) Magnesium methoxypropylate  2.0 g (0.010 mol)Aluminum methoxypropylate 25.0 g (0.085 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate and 2.00 g (0.005 mol) of rhodium acetylacetonate weredissolved in 200 mL of toluene, and the resulting solution was added tothe mixed alkoxide solution in the round bottomed flask to obtain aNdBaMgAlPtRh containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise to the solution inthe round bottomed flask over about fifteen minutes. Then, a brownviscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a NdBaMgAlPtRh composite oxide. Next,the pre-crystallization composition was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 650° C. in the air for two hours toobtain a powdery perovskite-type composite oxide comprisingNd_(0.80)Ba_(0.10)Mg_(0.10)Al_(0.85)Pt_(0.10)Rh_(0.05)O₃.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery perovskite-type composite oxide was addedthe powdery theta-alumina. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 6 mil per400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 28 g of the perovskite-type composite oxide and 50 gof the theta-alumina per one liter of the honeycomb carrier. Theresulting article was dried at 100° C. and baked at 500° C. to obtain anexhaust gas purifying catalyst. The resulting exhaust gas purifyingcatalyst contained 2.41 g of Pt and 0.66 g of Rh per one liter of thehoneycomb carrier.

Example PA-9

1) Production of Platinum Containing Perovskite-Type Composite OxideLanthanum nitrate 39.0 g (0.090 mol) Srontium nitrate 2.8 g (0.010 mol)Iron nitrate 23.0 g (0.057 mol) Manganese nitrate 10.9 g (0.038 mol)Dinitrodiammine platinum nitrate 11.48 g (corresponding solution havinga Pt content of 8.50% to 0.975 g (0.005 mol) by mass of Pt)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery perovskite-type composite oxidecomprising La_(0.90)Sr_(0.10)Fe_(0.57)Mn_(0.38)Pt_(0.05)O₃.

2) Production of Rhodium Containing Perovskite-Type Composite OxideLanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 18.4 g(0.057 mol) Manganese ethoxyethylate  8.9 g (0.038 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeMnRh containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a LaFeMnRh composite oxide. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for two hours to obtain a powderyperovskite-type composite oxide comprisingLa_(1.00)Fe_(0.57)Mn_(0.38)Rh_(0.05)O₃.

3) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of exhaust gas purifying Catalyst

To each of the above prepared powdery perovskite-type composite oxideswas added the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum. The mixture wasmixed with deionized water and further mixed with alumina sol to obtaina slurry. The slurry was injected into a honeycomb cordierite carrierhaving a size of 6 mil per 400 cells, a diameter of 80 mm and a lengthof 95 mm so as to homogeneously apply 60 g of the platinum containingperovskite-type composite oxide, 90 g of the rhodium containingperovskite-type composite oxide, and 100 g of the lanthanum containingtheta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The resulting exhaust gas purifying catalystcontained 2.39 g of Pt and 0.19 g of Rh per one liter of the honeycombcarrier.

Example PA-10

1) Production of Palladium Containing Perovskite-Type Composite OxideLanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a LaFePd composite oxide. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyperovskite-type composite oxide comprisingLa_(1.00)Fe_(0.95)Pd_(0.05)O₃.

2) Production of Rhodium Containing Perovskite-Type Composite OxideLanthanum nitrate 43.3 g (0.100 mol) Iron nitrate 38.4 g (0.095 mol)Rhodium nitrate solution having a Rh 11.5 g (corresponding content of4.478% by mass to 0.51 g (0.005 mol) of Rh)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery perovskite-type composite oxidecomprising La_(1.00)Fe_(0.95)Rh_(0.05)O₃.

3) Production of Exhaust Gas Purifying Catalyst

To each of the above prepared powdery perovskite-type composite oxideswas added the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum. The mixture wasmixed with deionized water and further mixed with alumina sol to obtaina slurry. The slurry was injected into a honeycomb cordierite carrierhaving a size of 6 mil per 400 cells, a diameter of 80 mm and a lengthof 95 mm so as to homogeneously apply 138 g of the palladium containingperovskite-type composite oxide, 9 g of the rhodium containingperovskite-type composite oxide, and 100 g of the lanthanum containingtheta-alumina per one liter of the honeycomb carrier. The resultingresulting article dried at 100° C. and baked at 500° C. to obtain anexhaust gas purifying catalyst. The resulting exhaust gas purifyingcatalyst contained 2.41 g of Pd and 0.19 g of Rh per one liter of thehoneycomb carrier.

Example PA-11

1) Production of Palladium Containing Perovskite-Type Composite OxideLanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a LaFePd composite oxide. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyperovskite-type composite oxide comprisingLa_(1.00)Fe_(0.95)Pd_(0.05)O₃.

2) Production of Platinum Containing Perovskite-Type Composite OxideLanthanum methoxyethylate 34.6 g (0.095 mol) Aluminum methoxyethylate21.4 g (0.085 mol) Manganese methoxyethylate  2.0 g (0.010 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.04 g (0.005 mol) of silveracetylacetonate and 1.965 g (0.005 mol) of platinum acetylacetonate weredissolved in 200 mL of toluene, and the resulting solution was added tothe mixed alkoxide solution in the round bottomed flask to obtain aLaAgAlMnPt containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a LaAgAlMnPt composite oxide. Next,the pre-crystallization composition was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 650° C. in the air for one hour toobtain a powdery perovskite-type composite oxide comprisingLa_(0.95)Ag_(0.05)Al_(0.85)Mn_(0.10)Pt_(0.05)O₃.

3) Production of Exhaust Gas Purifying Catalyst

To each of the above prepared powdery perovskite-type composite oxideswere added the powdery Rh supporting zirconia composite oxide(Production Example A1-1) comprising aZr_(0.79)Ce_(0.16)La_(0.01)Nd_(0.04) oxide supporting 0.50% by weight ofRh and the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum. The mixture wasmixed with deionized water and further mixed with alumina sol to obtaina slurry. The slurry was injected into a honeycomb cordierite carrierhaving a size of 6 mil per 400 cells, a diameter of 80 mm and a lengthof 95 mm so as to homogeneously apply 92 g of the palladium containingperovskite-type composite oxide, 11.2 g of the platinum containingperovskite-type composite oxide, 40 g of the Rh supporting zirconiacomposite oxide and 100 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 0.50 g of Pt, 2.00 g of Pd, and0.20 g of Rh per one liter of the honeycomb carrier.

Example QA-12

1) Production of Palladium Containing Perovskite-Type Composite OxideLanthanum nitrate 43.3 g (0.100 mol) Iron nitrate 36.4 g (0.090 mol)Aqueous palladium nitrate solution having 24.5 g (corresponding a Pdcontent of 4.399% by mass to 1.06 g (0.010 mol) of Pd)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous solution of citric acid and salts.

The aqueous solution of citric acid and salts was evaporated to drynessin a hot water bath at 60° C. to 80° C. with evacuation using a rotaryevaporator. After passage of about three hours and when the solutioncame into a starch-syrup-like state, the temperature of the hot waterbath was gradually raised, followed by drying at 250° C. in vacuum forone hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery perovskite-type composite oxidecomprising La_(1.00)Fe_(0.90)Pd_(0.10)O₃.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas purifying Catalyst

To the above prepared powdery perovskite-type composite oxide was addedthe powdery theta-alumina, followed by mixing in a mortar to obtain apowdery exhaust gas purifying catalyst comprising theLa_(1.00)Fe_(0.90)Pd_(0.10)O₃ perovskite-type composite oxide and thetheta-alumina.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:2.

Example QA-13

Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide and Production of Exhaust Gas Purifying CatalystLanthanum nitrate 43.3 g (0.100 mol) Iron nitrate 38.4 g (0.095 mol)Aqueous palladium nitrate solution having 12.1 g (corresponding a Pdcontent of 4.399% by mass to 0.53 g (0.005 mol) of Pd)

The above listed components were dissolved in 200 mL of deionized waterto obtain an aqueous mixed salt solution. Next, 73.4 g of a powderytheta-alumina was added to the aqueous mixed salt solution, followed bystirring. An aqueous solution of ammonium carbonate was added dropwisethereto up to pH 10. Then the coprecipitate was fully stirred for onehour, filtrated, washed with water, subjected to forced air drying at120° C. for twelve hours and baked at 700° C. in the air for three hoursto obtain a powdery exhaust gas purifying catalyst comprisingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:3.

Example QA-14

Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide and Production of Exhaust Gas Purifying CatalystLanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

To the homogeneous mixed solution was added 98.0 g of the powderylanthanum containing theta-alumina (Production Example C3) having alanthanum content of 4.0% by weight, followed by stirring, and 200 mL ofdeionized water was added dropwise to the solution over about fifteenminutes. Then, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of alanthanum containing theta-alumina with a homogeneously dispersed LaFePdcontaining perovskite-type composite oxide. Next, the mixture was placedon a petri dish, subjected to forced air drying at 60° C. for twentyfour hours and heat treated in an electric furnace at 800° C. in the airfor one hour to obtain a powdery exhaust gas purifying catalystcomprising lanthanum containing theta-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:4.

Example QA-15

Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide and Production of Exhaust Gas Purifying CatalystLanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

To the homogeneous mixed solution was added 24.5 g of the powderylanthanum containing theta-alumina (Production Example C3) containing4.0% by weight of lanthanum, followed by stirring, and 200 mL ofdeionized water was added dropwise to the solution over about fifteenminutes. Then, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of alanthanum containing theta-alumina with a homogeneously dispersed LaFePdcontaining perovskite-type composite oxide. Next, the mixture was placedon a petri dish, subjected to forced air drying at 60° C. for twentyfour hours and heat treated in an electric furnace at 800° C. in the airfor one hour to obtain a powdery exhaust gas purifying catalystcomprising lanthanum containing theta-alumina supporting a.La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

Example QA-16

Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide and Production of Exhaust Gas Purifying CatalystLanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 18.4g (0.057 mol) Manganese methoxypropylate  8.9 g (0.038 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 20 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeMnRh containing homogeneous mixed solution.

To the homogeneous mixed solution was added 220 g of the powderylanthanum containing theta-alumina (Production Example C2) containing2.0% by weight of lanthanum, followed by stirring, and 200 mL ofdeionized water was added dropwise to the solution over about fifteenminutes. Then, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of alanthanum containing theta-alumina with a homogeneously dispersedLaFeMnRh containing perovskite-type composite oxide. Next, the mixturewas placed on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 800° C. inthe air for one hour to obtain a powdery exhaust gas purifying catalystcomprising lanthanum containing theta-alumina supporting aLa_(1.00)Fe_(0.57)Mn_(0.38)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:9.

Example QA-17

Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide and Production of Exhaust Gas Purifying CatalystLanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 20 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

To the homogeneous mixed solution was added 36.8 g of the powderylanthanum containing theta-alumina (Production Example C4) containing10.0% by weight of lanthanum, followed by stirring, and 200 mL ofdeionized water was added dropwise to the solution over about fifteenminutes. Then, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of alanthanum containing theta-alumina with a homogeneously dispersed LaFeRhcontaining perovskite-type composite oxide. Next, the mixture was placedon a petri dish, subjected to forced air drying at 60° C. for twentyfour hours and heat treated in an electric furnace at 800° C. in the airfor one hour to obtain a powdery exhaust gas purifying catalystcomprising lanthanum containing theta-alumina supporting aLa_(1.00)Fe_(0.95)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:3.

Example QA-18

Supporting of Platinum Containing Perovskite-Type Composite Oxide byThermostable Oxide and Production of Exhaust Gas Purifying CatalystLanthanum inethoxypropylate 38.6 g (0.095 mol) Iron methoxypropylate18.4 g (0.057 mol) Manganese methoxypropylate  8.9 g (0.038 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.965 g (0.005 mol) of platinumacetylacetonate and 1.53 g (0.005 mol) of silver acetylacetonate weredissolved in 40 mL of toluene, and the resulting solution was added tothe mixed alkoxide solution in the round bottomed flask to obtain aLaAgFeMnPt containing homogeneous mixed solution.

To the homogeneous mixed solution was added 24.5 g of the powderylanthanum containing theta-alumina (Production Example C4) containing10.0% by weight of lanthanum, followed by stirring, and 200 mL ofdeionized water was added dropwise to the solution over about fifteenminutes. Then, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of alanthanum containing theta-alumina with a homogeneously dispersedLaAgFeMnPt containing perovskite-type composite oxide. Next, the mixturewas placed on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 800° C. inthe air for one hour to obtain a powdery exhaust gas purifying catalystcomprising lanthanum containing theta-alumina supporting aLa_(0.95)Ag_(0.05)Fe_(0.57)Mn_(0.38)Pt_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

Example QA-19

Supporting of Platinum Containing Perovskite-Type Composite Oxide byThermostable Oxide and Production of Exhaust Gas Purifying CatalystLanthanum methoxypropylate 36.6 g (0.090 mol) Calcium methoxypropylate 2.2 g (0.010 mol) Iron methoxypropylate 29.1 g (0.090 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate was dissolved in 40 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

To the homogeneous mixed solution was added 98.7 g of the powderytheta-alumina, followed by stirring, and 200 mL of deionized water wasadded dropwise to the solution over about fifteen minutes. Then, a brownviscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture oftheta-alumina with a homogeneously dispersed LaCaFePt containingperovskite-type composite oxide. Next, the mixture was placed on a petridish, subjected to forced air drying at 60° C. for twenty four hours andheat treated in an electric furnace at 800° C. in the air for one hourto obtain a powdery exhaust gas purifying catalyst comprisingtheta-alumina supporting a La_(0.90)Ca_(0.10)Fe_(0.90)Pt_(0.10)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:4.

Example RA-20

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

A powdery zirconia composite oxide (Production Example A2) comprising aZr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05) oxide was dispersed in 200 mL oftoluene and the homogeneous mixed solution in the round bottomed flaskwas added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFePdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05) oxide supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide was added the powdery theta-alumina. Themixture was mixed with deionized water and further mixed with aluminasol to obtain a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 150 g of thezirconia composite oxide supporting the perovskite-type composite oxideand 150 g of theta-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to obtain anexhaust gas purifying catalyst. The resulting exhaust gas purifyingcatalyst contained 0.66 g of Pd per one liter of the honeycomb carrier.

Example RA-21

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 18.4 g (0.057 mol) Manganese ethoxyethylate  8.9 g (0.038mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeMnPd containing homogeneous mixed solution.

A powdery zirconia composite oxide (Production Example A3) comprising aZr_(0.50)Ce_(0.40)La_(0.05)Nd_(0.05) oxide was dispersed in 200 mL oftoluene and the homogeneous mixed solution in the round bottomed flaskwas added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFeMnPdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.50)Ce_(0.40)La_(0.05)Nd_(0.05) oxide supporting aLa_(1.00)Fe_(0.57)Mn_(0.38)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B1-1) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.25% by weight of Pt andthe powdery theta-alumina. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 150 g of the zirconia composite oxide supporting theperovskite-type composite oxide, 60 g of the Pt supporting ceriacomposite oxide, and 90 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 0.15 g of Pt and 0.66 g of Pdper one liter of the honeycomb carrier.

Example RA-22

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 18.4 g (0.057 mol) Manganese ethoxyethylate  8.9 g (0.038mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeMnPd containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A4)comprising Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFeMnPdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03)oxide supporting a La_(1.00)Fe_(0.57)Mn_(0.38)Pd_(0.05)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide were added the powdery ceria compositeoxide (Production Example B1) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide and the powdery Rh supporting theta-alumina (Production ExampleC7) comprising theta-alumina supporting 0.188% by weight of Rh. Themixture was mixed with deionized water and further mixed with aluminasol to obtain a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 150 g of thezirconia composite oxide supporting the perovskite-type composite oxide,70 g of the ceria composite oxide, and 80 g of the Rh supportingtheta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The resulting exhaust gas purifying catalystcontained 0.66 g of Pd and 0.15 g of Rh per one liter of the honeycombcarrier.

Example RA-23

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A5)comprising a Zr_(0.70)Ce_(0.20)La_(0.05)Y_(0.05) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFePdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.70)Ce_(0.20)La_(0.05)Y_(0.05) oxide supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide were added the powdery Pt—Rh supportingzirconia composite oxide (Production Example A6-1) comprisingZr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide supporting 0.2% by weight ofPt and 0.3% by weight of Rh, the powdery ceria composite oxide(Production Example B1) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide,and the powdery Pt—Rh supporting theta-alumina (Production Example C8-1)supporting 0.4% by weight of Pt and 0.1% by weight of Rh. The mixturewas mixed with deionized water and further mixed with alumina sol toobtain a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 3 mil per 600 cells, a diameter of 86 mm and alength of 104 mm so as to homogeneously apply 150 g of the zirconiacomposite oxide supporting the perovskite-type composite oxide, 30 g ofthe Pt—Rh supporting zirconia composite oxide, 50 g of the ceriacomposite oxide, and 60 g of the Pt—Rh supporting theta-alumina per oneliter of the honeycomb carrier. The resulting article dried at 100° C.and baked at 500° C. to obtain an exhaust gas purifying catalyst. Theresulting exhaust gas purifying catalyst contained 0.30 g of Pt, 0.66 gof Pd, and 0.15 g of Rh per one liter of the honeycomb carrier.

Example RA-24

1) Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol) Ceriumethoxyethylate  4.1 g (0.010 mol) Iron ethoxyethylate 29.1 g (0.090 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 4.00 g (0.010 mol) of rhodiumacetylacetonate was dissolved in 200 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCeFeRh containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A7)comprising a Zr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaCeFeRhcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05) oxide supporting aLa_(0.9)Ce_(0.10)Fe_(0.09)Rh_(0.10)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 1:9.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide was added the powdery theta-alumina. Themixture was mixed with deionized water and further mixed with aluminasol to obtain a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 150 g of thezirconia composite oxide supporting the perovskite-type composite oxideand 150 g of the theta-alumina per one liter of the honeycomb carrier.The resulting article dried at 100° C. and baked at 500° C. to obtain anexhaust gas purifying catalyst. The resulting exhaust gas purifyingcatalyst contained 0.63 g of Rh per one liter of the honeycomb carrier.

Example RA-25

1) Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol) Ceriumethoxyethylate  4.1 g (0.010 mol) Iron ethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCeFeRh containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C4) containing 10.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaCeFeRh composite oxide. Next, the lanthanumcontaining theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery lanthanumcontaining theta-alumina supporting aLa_(0.90)Ce_(0.10)Fe_(0.95)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:8.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery lanthanum containing theta-aluminasupporting the perovskite-type composite oxide were added the powderyceria composite oxide (Production Example B1) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide and the powdery Pt—Rh supportingtheta-alumina (Production Example C8-2) supporting 0.50% by weight of Ptand 0.10% by weight of Rh. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 150 g of the lanthanum containing theta-aluminasupporting the perovskite-type composite oxide, 90 g of the ceriacomposite oxide, and 60 g of the Pt—Rh supporting theta-alumina per oneliter of the honeycomb carrier. The resulting article dried at 100° C.and baked at 500° C. to obtain an exhaust gas purifying catalyst. Theresulting exhaust gas purifying catalyst contained 0.30 g of Pt and 0.69g (0.63 g in the perovskite-type composite oxide, 0.06 g on thetheta-alumina) of Rh per one liter of the honeycomb carrier.

Example RA-26

1) Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

Separately, the powdery SrZrO₃ (Production Example Dl) was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain SrZrO₃ with adispersed pre-crystallization composition of a LaFeRh composite oxide.Next, SrZrO₃ with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery SrZrO₃ supporting aLa_(1.00)Fe_(0.95)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to SrZrO₃ of 2:8.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery SrZrO₃ supporting the perovskite-typecomposite oxide were added the powdery Pt—Rh supporting zirconiacomposite oxide (Production Example A1-2) comprising aZr_(0.79)Ce_(0.16)La_(0.01)Nd_(0.04) oxide supporting 0.15% by weight ofPt and 0.15% by weight of Rh, the powdery Pt supporting ceria compositeoxide (Production Example B2-1) comprising a Ce_(0.40)Zr_(0.50)Y_(0.10)oxide supporting 0.20% by weight of Pt and the powdery Pt—Rh supportingtheta-alumina (Production Example C8-2) comprising theta-aluminasupporting 0.50% by weight of Pt and 0.10% by weight of Rh. The mixturewas mixed with deionized water and further mixed with alumina sol toobtain a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 3 mil per 600 cells, a diameter of 86 mm and alength of 104 mm so as to homogeneously apply 150 g of SrZrO₃ supportingthe perovskite-type composite oxide, 60 g of the Pt—Rh supportingzirconia composite oxide, 30 g of the Pt supporting ceria compositeoxide, and 60 g of the Pt—Rh supporting theta-alumina per one liter ofthe honeycomb carrier. The resulting article dried at 100° C. and bakedat 500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 0.45 g (0.06 g on the ceriacomposite oxide, 0.09 g on the zirconia composite oxide, 0.30 g on thetheta-alumina) of Pt and 0.78 g (0.63 g in the perovskite-type compositeoxide, 0.09 g on the zirconia composite oxide, 0.06 g on thetheta-alumina) of Rh per one liter of the honeycomb carrier.

Example RA-27

1) Supporting of Platinum Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol) Calciumethoxyethylate  2.2 g (0.010 mol) Iron ethoxyethylate 29.1 g (0.090 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate was dissolved in 200 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A7)comprising a Zr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaCaFePtcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising Zr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05)oxide supporting a La_(0.90)Ca_(0.10)Fe_(0.90)Pt_(0.10)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 1:9.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared zirconia composite oxide supporting theperovskite-type composite oxide was added the powdery theta-alumina. Themixture was mixed with deionized water and further mixed with aluminasol to obtain a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 75 g of thezirconia composite oxide supporting the perovskite-type composite oxideand 150 g of the theta-alumina per one liter of the honeycomb carrier.The resulting article dried at 100° C. and baked at 500° C. to obtain anexhaust gas purifying catalyst. The resulting exhaust gas purifyingcatalyst contained 0.59 g of Pt per one liter of the honeycomb carrier.

Example RA-28

1) Supporting of Platinum Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol) Calciumethoxyethylate  2.2 g (0.010 mol) Iron ethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.965 g (0.005 mol) of platinumacetylacetonate was dissolved in 200 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C4) containing 10.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaCaFePt composite oxide. Next, the lanthanumcontaining theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery lanthanumcontaining theta-alumina supporting aLa_(0.90)Ca_(0.10)Fe_(0.95)Pt_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:8.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery lanthanum containing theta-aluminasupporting the perovskite-type composite oxide were added the powderyceria composite oxide (Production Example B1) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide and the powdery Pt—Rh supportingtheta-alumina (Production Example C8-3) comprising theta-aluminasupporting 0.50% by weight of Pt and 0.17% by weight of Rh. The mixturewas mixed with deionized water and further mixed with alumina sol toobtain a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 3 mil per 600 cells, a diameter of 86 mm and alength of 104 mm so as to homogeneously apply 75 g of the lanthanumcontaining theta-alumina supporting the perovskite-type composite oxide,90 g of the ceria composite oxide, and 60 g of the Pt—Rh supportingtheta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The resulting exhaust gas purifying catalystcontained 0.91 g (0.61 g in the perovskite-type composite oxide, 0.30 gon the theta-alumina) of Pt and 0.10 g of Rh per one liter of thehoneycomb carrier.

Example RA-29

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum nitrate 43.3 g (0.100 mol) Iron nitrate23.0 g (0.057 mol) Manganese nitrate 10.9 g (0.038 mol) Palladiumnitrate solution having a 12.1 g (corresponding Pd content of 4.399% bymass to 0.53 g (0.005 mol) of Pd)

The above listed components were dissolved in 100 mL of pure water,followed by homogeneous mixing to obtain an aqueous mixed salt solution.Separately, 50.4 g (0.24 mol) of citric acid was dissolved in purewater, and the solution was added to the aqueous mixed salt solution toobtain an aqueous LaFeMnPd containing solution of citric acid and salts.

To the powdery zirconia composite oxide (Production Example A8)comprising a Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide were added 200 mLof pure water and the aqueous LaFeMnPd containing solution of citricacid and salts, followed by stirring. The mixture was evaporated todryness in a hot water bath at 60° C. to 80° C. with evacuation using arotary evaporator. After passage of about three hours and when thesolution came into a starch-syrup-like state, the temperature of the hotwater bath was gradually raised, followed by drying at 250° C. in vacuumfor one hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 300° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery zirconia composite oxidecomprising Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide supporting aLa_(1.00)Fe_(0.57)Mn_(0.38)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2) Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol) Ceriumethoxyethylate  4.1 g (0.010 mol) Iron ethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCeFeRh containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaCeFeRh composite oxide. Next, the lanthanumcontaining theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery lanthanumcontaining theta-alumina supporting aLa_(0.90)Ce_(0.10)Fe_(0.95)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:8.

3) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide and powdery lanthanum theta-aluminasupporting the perovskite-type composite oxide were added the powderyceria composite oxide (Production Example B1-2) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weight of Pt, andthe powdery theta-alumina. The mixture was mixed with deionized waterand further mixed with alumina sol to obtain a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 6 mil per400 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 50 g of the zirconia composite oxide supporting thepalladium containing perovskite-type composite oxide, 50 g of thelanthanum containing theta-alumina supporting the rhodium containingperovskite-type composite oxide, 60 g of the Pt supporting ceriacomposite oxide, and 40 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 0.30 g of Pt, 0.22 g of Pd, and0.26 g of Rh per one liter of the honeycomb carrier.

Example RA-29-1

1) Production of Palladium Containing Perovskite-Type Composite OxideLanthanum nitrate 43.3 g (0.100 mol) Iron nitrate 40.4 g (0.100 mol)

An aqueous solution prepared by dissolving the above lanthanum nitratein 100 mL of pure water and an aqueous solution prepared by dissolvingthe above iron nitrate in 30 mL of ion-exchanged water werehomogeneously mixed to obtain an aqueous mixed salt solution.Separately, 38.4 g (0.20 mol) of citric acid was dissolved inion-exchanged water, and the solution was added to the aqueous mixedsalt solution to obtain an aqueous LaFe containing solution of citricacid and salts.

The aqueous LaFe containing solution of citric acid and salts wasevaporated to dryness in a hot water bath at 60° C. to 80° C. withevacuation using a rotary evaporator. After passage of about three hoursand when the solution came into a starch-syrup-like state, thetemperature of the hot water bath was gradually raised, followed bydrying at 250° C. in vacuum for one hour to obtain a citrate complex.

The above-prepared citrate complex was baked at 400° C. in the air forthree hours, pulverized in a mortar and baked again at 700° C. in theair for three hours to obtain a powdery perovskite-type composite oxidecomprising La_(1.00)Fe_(1.00)O₃.

The resulting powdery perovskite-type composite oxide was impregnatedwith a palladium nitrate solution, dried at 100° C. and baked at 500° C.to obtain a powdery palladium supporting perovskite-type composite oxidecontaining 2.20% by weight of Pd.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery palladium supporting perovskite-typecomposite oxide supporting Pd were added the powdery Pt—Rh supportingzirconia composite oxide (Production Example A6-1) comprising aZr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide supporting 0.20% by weight ofPt and 0.30% by weight of Rh, the powdery ceria composite oxide(Production Example B1-3) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxidesupporting 1.00% by weight of Pt, and the powdery theta-alumina. Themixture was mixed with deionized water and further mixed with aluminasol to obtain a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 6 mil per 400 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 30 g of thepalladium supporting perovskite-type composite oxide, 40 g of the Pt—Rhsupporting zirconia composite oxide, 50 g of the Pt supporting ceriacomposite oxide, and 50 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 0.58 g of Pt, 0.66 g of Pd, and0.12 g of Rh per one liter of the honeycomb carrier.

Example RA-30

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 800° C. inthe air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery lanthanum containing theta-aluminasupporting the perovskite-type composite oxide were added the powderyPt—Rh supporting zirconia composite oxide (Production Example A6-2)comprising a Zr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide supporting 1.00%by weight of Pt and 1.00% by weight of Rh, the powdery Pt supportingceria composite oxide (Production Example B1-3) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 1.00% by weight of Pt, andthe powdery Pt—Rh supporting theta-alumina (Production Example C8-4)supporting 0.57% by weight of Pt and 0.14% by weight of Rh. The mixturewas mixed with deionized water and further mixed with alumina sol toobtain a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 3 mil per 600 cells, a diameter of 86 mm and alength of 104 mm so as to homogeneously apply 30 g of the lanthanumcontaining theta-alumina supporting the perovskite-type composite oxide,30 g of the Pt—Rh supporting zirconia composite oxide, 80 g of the Ptsupporting ceria composite oxide, and 70 g of the Pt—Rh supportingtheta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The resulting exhaust gas purifying catalystcontained 1.50 g of Pt, 0.33 g of Pd, and 0.40 g of Rh per one liter ofthe honeycomb carrier.

Example RA-31

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 800° C. inthe air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery lanthanum containing theta-aluminasupporting the perovskite-type composite oxide were added the powderyceria composite oxide (Production Example B1-3) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 1.00% by weight of Pt andthe powdery Pt—Rh supporting gamma-alumina (Production Example C13-1)comprising gamma-alumina supporting 1.00% by weight of Pt and 0.57% byweight of Rh. The mixture was mixed with deionized water and furthermixed with alumina sol to obtain a slurry. The slurry was injected intoa honeycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply 30g of the lanthanum containing theta-alumina supporting theperovskite-type composite oxide, 80 g of the Pt supporting ceriacomposite oxide, and 70 g of the Pt—Rh supporting gamma-alumina per oneliter of the honeycomb carrier. The resulting article dried at 100° C.and baked at 500° C. to obtain an exhaust gas purifying catalyst. Theresulting exhaust gas purifying catalyst contained 1.50 g of Pt, 0.33 gof Pd, and 0.40 g of Rh per one liter of the honeycomb carrier.

Example RA-32

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery alpha-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain alpha-alumina with adispersed pre-crystallization composition of a LaFePd composite oxide.Next, the alpha-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 800° C. in the air for one hour to obtain powdery alpha-aluminasupporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the alpha-alumina of 1:2.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of exhaust gas purifying Catalyst

To the above prepared powdery alpha-alumina supporting theperovskite-type composite oxide were added the powdery Pt—Rh supportingzirconia composite oxide (Production Example A6-2) comprising aZr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide supporting 1.00% by weight ofPt and 1.00% by weight of Rh, the powdery Pt supporting ceria compositeoxide (Production Example B1-9) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide supporting 1.38% by weight of Pt and the powdery gamma-alumina.The mixture was mixed with deionized water and further mixed withalumina sol to obtain a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 45 g of thealpha-alumina supporting the perovskite-type composite oxide, 40 g ofthe Pt—Rh supporting zirconia composite oxide, 80 g of the Pt supportingceria composite oxide, and 70 g of the gamma-alumina per one liter ofthe honeycomb carrier. The resulting article dried at 100° C. and bakedat 500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 1.50 g of Pt, 0.33 g of Pd, and0.40 g of Rh per one liter of the honeycomb carrier.

Example RC-1

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A4)comprising a Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFePdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

1)-2 Production of Inner Layer

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B1-4) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.30% by weight of Pt, andthe powdery theta-alumina. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 75 g of the zirconia composite oxide supporting theperovskite-type composite oxide, 50 g of the Pt supporting ceriacomposite oxide, and 70 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting zirconia composite oxide (ProductionExample A6-3) comprising a Zr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxidesupporting 0.30% by weight of Pt and 1.40% by weight of Rh, the powderyPt supporting ceria composite oxide (Production Example B1-2) comprisinga Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weight of Pt, andthe powdery theta-alumina were mixed. The resulting mixture was furthermixed with deionized water and then mixed with alumina sol to form aslurry. The slurry was injected into the honeycomb cordierite carrierhaving a size of 3 mil per 600 cells, a diameter of 86 mm and a lengthof 104 mm so as to homogeneously apply, to a surface of the inner layer,50 g of the Pt—Rh supporting zirconia composite oxide, 30 g of the Ptsupporting ceria composite oxide, and 50 g of the theta-alumina per oneliter of the honeycomb carrier. The resulting article dried at 100° C.and baked at 500° C. to form an outer layer. Thus, an exhaust gaspurifying catalyst was produced.

The resulting exhaust gas purifying catalyst contained 0.15 g of Pt and0.33 g of Pd in the inner layer, and 0.30 g of Pt and 0.70 g of Rh inthe outer layer, respectively, per one liter of the honeycomb carrier.

Example RC-2

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery SrZrO₃ (Production Example Dl) was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain SrZrO₃ with adispersed pre-crystallization composition of a LaFePd composite oxide.Next, SrZrO₃ with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery SrZrO₃ supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to SrZrO₃ of 2:8.

1)-2 Production of Inner Layer

To the above prepared powdery SrZrO₃ supporting a perovskite-typecomposite oxide were added the powdery Pt supporting ceria compositeoxide (Production Example B1-4) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide supporting 0.30% by weight of Pt, the powdery theta-alumina andthe powdery BaSO₄. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 75 g of SrZrO₃ supporting the perovskite-typecomposite oxide, 30 g of the Pt supporting ceria composite oxide, 70 gof the theta-alumina, and 20 g of BaSO₄ per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting zirconia composite oxide (ProductionExample A6-3) comprising a Zr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxidesupporting 0.30% by weight of Pt and 1.40% by weight of Rh, the powderyPt supporting ceria composite oxide (Production Example B1-2) comprisinga Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weight of Pt, andthe powdery theta-alumina were mixed. The resulting mixture was furthermixed with deionized water and then mixed with alumina sol to form aslurry. The slurry was injected into a honeycomb cordierite carrierhaving a size of 3 mil per 600 cells, a diameter of 86 mm and a lengthof 104 mm thereby to homogeneously apply, to a surface of the innerlayer, 50 g of the Pt—Rh supporting zirconia composite oxide, 30 g ofthe Pt supporting ceria composite oxide, and 50 g of the theta-aluminaper one liter of the honeycomb carrier. The resulting article dried at100° C. and baked at 500° C. to form an outer layer. Thus, an exhaustgas purifying catalyst was produced.

The resulting exhaust gas purifying catalyst contained 0.15 g of Pt and0.33 g of Pd in the inner layer, and 0.30 g of Pt and 0.70 g of Rh inthe outer layer, respectively, per one liter of the honeycomb carrier.

Example RC-3

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain apre-crystallization composition of a LaFePd composite oxide. Next, thepre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyperovskite-type composite oxide comprisingLa_(1.00)Fe_(0.95)Pd_(0.05)O₃.

1)-2 Production of Inner Layer

To the above prepared perovskite-type composite oxide were added thepowdery Pt supporting ceria composite oxide (Production Example B1-4)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.30% by weightof Pt, the powdery theta-alumina, and a powdery BaSO₄. The resultingmixture was further mixed with deionized water and then mixed withalumina sol to form a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 30 g of theperovskite-type composite oxide, 50 g of the Pt supporting ceriacomposite oxide, 90 g of the theta-alumina, and 20 g of BaSO₄ per oneliter of the honeycomb carrier. The resulting article dried at 100° C.and baked at 500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting zirconia composite oxide (ProductionExample A6-3) comprising a Zr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxidesupporting 0.30% by weight of Pt and 1.40% by weight of Rh, the powderyPt supporting ceria composite oxide (Production Example B1-2) comprisinga Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weight of Pt, andthe powdery theta-alumina were mixed. The resulting mixture was furthermixed with deionized water and then mixed with alumina sol to form aslurry. The slurry was injected into the honeycomb cordierite carrierhaving a size of 3 mil per 600 cells, a diameter of 86 mm and a lengthof 104 mm so as to homogeneously apply, to a surface of the inner layer,50 g of the Pt—Rh supporting zirconia composite oxide, 40 g of the Ptsupporting ceria composite oxide, and 50 g of the theta-alumina per oneliter of the honeycomb carrier. The resulting article dried at 100° C.and baked at 500° C. to form an outer layer. Thus, an exhaust gaspurifying catalyst was produced.

The resulting exhaust gas purifying catalyst contained 0.15 g of Pt and0.66 g of Pd in the inner layer, and 0.35 g of Pt and 0.70 g of Rh inthe outer layer, respectively, per one liter of the honeycomb carrier.

Example RC-4

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A4)comprising a Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFePdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

1)-2 Production of Inner Layer

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B1-5) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.80% by weight of Pt, andthe powdery theta-alumina. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 75 g of the zirconia composite oxide supporting theperovskite-type composite oxide, 20 g of the Pt supporting ceriacomposite oxide, and 90 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting zirconia composite oxide (ProductionExample A9-1) comprising a Zr_(0.80)Ce_(0.15)La_(0.02)Nd_(0.03) oxidesupporting 0.27% by weight of Pt and 1.33% by weight of Rh, the powderyPt supporting ceria composite oxide (Production Example B1-5) comprisinga Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.80% by weight of Pt, andthe powdery Pt—Rh supporting theta-alumina (Production Example C8-5)comprising theta-aluminum supporting 0.43% by weight of Pt and 0.21% byweight of Rh were mixed. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into the honeycomb cordierite carrier having a sizeof 3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm so asto homogeneously apply, to a surface of the inner layer, 30 g of thePt—Rh supporting zirconia composite oxide, 30 g of the Pt supportingceria composite oxide, and 70 g of the Pt—Rh supporting theta-aluminaper one liter of the honeycomb carrier. The resulting article dried at100° C. and baked at 500° C. to form an outer layer. Thus, an exhaustgas purifying catalyst was produced.

The resulting exhaust gas purifying catalyst contained 0.16 g of Pt and0.33 g of Pd in the inner layer, and 0.62 g of Pt and 0.55 g of Rh inthe outer layer, respectively, per one liter of the honeycomb carrier.

Example RC-5

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 31.0 g (0.096 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.22 g (0.004 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain theta-alumina with adispersed pre-crystallization composition of a LaFePd composite oxide.Next, the theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery theta-aluminasupporting a La_(1.00)Fe_(0.96)Pd_(0.04)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 2:8.

1)-2 Production of Inner Layer

To the above prepared theta-alumina supporting the perovskite-typecomposite oxide were added the powdery Pt supporting ceria compositeoxide (Production Example B1-5) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide supporting 0.80% by weight of Pt, and the powdery theta-alumina.The resulting mixture was further mixed with deionized water and thenmixed with alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply 75g of the theta-alumina supporting the perovskite-type composite oxide,20 g of the Pt supporting ceria composite oxide, and 90 g of thetheta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Rh supporting zirconia composite oxide (Production ExampleA9-2) comprising a Zr_(0.80)Ce_(0.15)La_(0.02)Nd_(0.03) oxide supporting0.83% by weight of Rh, the powdery Pt supporting ceria composite oxide(Production Example B1-5) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxidesupporting 0.80% by weight of Pt, and the powdery Pt—Rh supportingtheta-alumina (Production Example C8-5) comprising theta-aluminasupporting 0.43% by weight of Pt and 0.21% by weight of Rh were mixed.The resulting mixture was further mixed with deionized water and thenmixed with alumina sol to form a slurry. The slurry was injected intothe honeycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply,to a surface of the inner layer, 30 g of the Rh supporting zirconiacomposite oxide, 30 g of the Pt supporting ceria composite oxide, and 70g of the Pt—Rh supporting theta-alumina per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an outer layer. Thus, an exhaust gas purifying catalyst wasproduced.

The resulting exhaust gas purifying catalyst contained 0.16 g of Pt and0.26 g of Pd in the inner layer, and 0.54 g of Pt and 0.40 g of Rh inthe outer layer, respectively, per one liter of the honeycomb carrier.

Example RC-6

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a theta-alumina witha dispersed pre-crystallization composition of a LaFePd composite oxide.Next, the theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery theta-aluminasupporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:1.

1)-2 Production of Inner Layer

To the above prepared powdery theta-alumina supporting theperovskite-type composite oxide were added the powdery ceria compositeoxide (Production Example B1) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide, and the powdery BaSO₄. The resulting mixture was further mixedwith deionized water and then mixed with alumina sol to form a slurry.The slurry was injected into a honeycomb cordierite carrier having asize of 3 mil per 600 cells, a diameter of 86 mm and a length of 104 mmso as to homogeneously apply 50 g of the theta-alumina supporting theperovskite-type composite oxide, 30 g of the ceria composite oxide, and20 g of BaSO₄ per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to form an inner layer.

2) Formation of Outer Layer

2)-1 Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

Separately, the powdery LaAlO₃ (Production Example E1) was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain LaAlO₃ with adispersed pre-crystallization composition of a LaFeRh composite oxide.Next, the LaAlO₃ with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery LaAlO₃ supporting aLa_(1.00)Fe_(0.95)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to LaAlO₃ of 2:8.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery LaAlO₃ supporting perovskite-typecomposite oxide were added the powdery Pt supporting ceria compositeoxide (Production Example B3-1) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide supporting 1.33% by weight of Pt, and the powdery theta-alumina.The resulting mixture was further mixed with deionized water and thenmixed with alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm thereby to homogeneously apply,to a surface of the inner layer, 95 g of LaAlO₃ supporting theperovskite-type composite oxide, 30 g of the Pt supporting ceriacomposite oxide, and 30 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an outer layer. Thus, an exhaust gas purifying catalystwas produced.

The resulting exhaust gas purifying catalyst contained 0.80 g of Pd inthe inner layer, and 0.40 g of Pt, and 0.40 g of Rh in the outer layer,respectively, per one liter of the honeycomb carrier.

Example RC-7

1) Formation of Inner Layer

To the powdery Pt supporting ceria composite oxide (Production ExampleB2-1) comprising a Ce_(0.40)Zr_(0.50)Y_(0.10) oxide supporting 0.20% byweight of Pt was added the powdery Pd supporting theta-alumina(Production Example C9-1) comprising theta-alumina supporting 0.40% byweight of Pd. The resulting mixture was further mixed with deionizedwater and then mixed with alumina sol to form a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 30 g of the Pt supporting ceria composite oxide and50 g of the Pd supporting theta-alumina per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an inner layer.

2) Formation of Outer Layer

2)-1 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol)Strontium ethoxyethylate  2.7 g (0.010 mol) Iron ethoxyethylate 29.1 g(0.090 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.965 g (0.005 mol) of platinumacetylacetonate and 2.00 g (0.005 mol) of rhodium acetylacetonate weredissolved in 100 mL of toluene, and the resulting solution was added tothe mixed alkoxide solution in the round bottomed flask to obtain aLaSrFePtRh containing homogeneous mixed solution.

Separately, the powdery SrZrO₃ (Production Example Dl) was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain SrZrO₃ with adispersed pre-crystallization composition of a LaSrFePtRh compositeoxide. Next, SrZrO₃ with the dispersed pre-crystallization compositionwas placed on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery SrZrO₃ supporting aLa_(0.90)Sr_(0.10)Fe_(0.90)Pt_(0.05)Rh_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to SrZrO₃ of 2:8.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery SrZrO₃ supporting the perovskite-typecomposite oxide was added the powdery Pt—Rh supporting zirconiacomposite oxide (Production Example A1-2) comprising aZr_(0.79)Ce_(0.16)La_(0.01)Nd_(0.04) oxide supporting 0.15% by weight ofPt and 0.15% by weight of Rh. The resulting mixture was further mixedwith deionized water and then mixed with alumina sol to form a slurry.The slurry was injected into a honeycomb cordierite carrier having asize of 3 mil per 600 cells, a diameter of 86 mm and a length of 104 mmthereby to homogeneously apply, to a surface of the inner layer, 75 g ofSrZrO₃ supporting the perovskite-type composite oxide and 60 g of thePt—Rh supporting zirconia composite oxide per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an outer layer. Thus, an exhaust gas purifying catalyst wasproduced.

The resulting exhaust gas purifying catalyst contained 0.06 g of Pt and0.20 g of Pd in the inner layer, and 0.68 g (0.59 g in theperovskite-type composite oxide, 0.09 g on the zirconia composite oxide)of Pt and 0.40 g (0.31 g in the perovskite-type composite oxide, 0.09 gon the zirconia composite oxide) of Rh in the outer layer, respectively,per one liter of the honeycomb carrier.

Example RC-8

1) Formation of Inner Layer

To the powdery Pd supporting gamma-alumina (Production Example C11-1)supporting 1.60% by weight of Pd were added the powdery ceria compositeoxide (Production Example B3) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide and the powdery BaSO₄. The resulting mixture was further mixedwith deionized water and then mixed with alumina sol to form a slurry.The slurry was injected into a honeycomb cordierite carrier having asize of 3 mil per 600 cells, a diameter of 86 mm and a length of 104 mmso as to homogeneously apply 50 g of the Pd supporting gamma-alumina, 30g of the ceria composite oxide, and 20 g of BaSO₄ per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an inner layer.

2) Formation of Outer Layer

2)-1 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol)Strontium ethoxyethylate  2.7 g (0.010 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.965 g (0.005 mol) of platinumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaSrFePt containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A7)comprising a Zr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaSrFePtcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a zirconiacomposite oxide comprising a Zr_(0.60)Ce_(0.30)La_(0.05)Y_(0.05) oxidesupporting a La_(0.90)Sr_(0.10)Fe_(0.95)Pt_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B3-2) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt andthe powdery Pt—Rh supporting theta-alumina (Production Example C8-6)comprising theta-alumina supporting 0.33% by weight of Pt and 1.33% byweight of Rh. The resulting mixture was further mixed with deionizedwater and then mixed with alumina sol to form a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm thereby tohomogeneously apply, to a surface of the inner layer, 63 g of thezirconia composite oxide supporting the perovskite-type composite oxide,30 g of the Pt supporting ceria composite oxide, and 30 g of the Pt—Rhsupporting theta-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an outerlayer. Thus, an exhaust gas purifying catalyst was produced.

The exhaust gas purifying catalyst contained 0.80 g of Pd in the innerlayer, and 0.70 g of Pt and 0.40 g of Rh in the outer layer,respectively, per one liter of the honeycomb carrier.

Example RC-9

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A4)comprising a Zr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFePdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.65)Ce_(0.30)La_(0.02)Y_(0.03) oxide supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

1)-2 Production of Inner Layer

To the above prepared powdery zirconia composite oxide supporting theperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B1-2) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weight of Pt andthe powdery lanthanum containing theta-alumina (Production Example C3)containing 4.0% by weight of lanthanum. The resulting mixture wasfurther mixed with deionized water and then mixed with alumina sol toform a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 6 mil per 400 cells, a diameter of 86 mm and alength of 104 mm so as to homogeneously apply 50 g of zirconia compositeoxide supporting the perovskite-type composite oxide, 30 g of the Ptsupporting ceria composite oxide, and 30 g of the lanthanum containingtheta-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to form an inner layer.

2) Formation of Outer Layer

2)-1 Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 12.3 g (0.038 mol) Aluminum ethoxyethylate 11.2 g (0.038mol) Manganese ethoxyethylate  4.4 g (0.019 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeAlMnRh containing homogeneous mixed solution.

Separately, the powdery SrZrO₃ (Production Example Dl) was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain SrZrO₃ with adispersed pre-crystallization composition of a LaFeAlMnRh compositeoxide. Next, SrZrO₃ with the dispersed pre-crystallization compositionwas placed on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery SrZrO₃ supporting aLa_(1.00)Fe_(0.38)Al_(0.38)Mn_(0.19)Rh_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to SrZrO₃ of 2:8.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery SrZrO₃ supporting the perovskite-typecomposite oxide was added the powdery Pt—Rh supporting lanthanumcontaining theta-alumina (Production Example C3-1) comprising alanthanum containing theta-alumina (lanthanum content: 4.0% by weight)supporting 1.00% by weight of Pt and 0.17% by weight of Rh. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 6 mil per 400 cells, adiameter of 86 mm and a length of 104 mm thereby to homogeneously apply,to a surface of the inner layer, 50 g of SrZrO₃ supporting theperovskite-type composite oxide and 60 g of the Pt—Rh supportinglanthanum containing theta-alumina per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an outer layer. Thus, an exhaust gas purifying catalyst wasproduced.

The resulting exhaust gas purifying catalyst contained 0.75 g of Pt,0.22 g of Pd, and 0.32 g of Rh per one liter of the honeycomb carrier.

Example RC-10

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 31.0 g (0.096 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.22 g (0.004 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.96)Pd_(0.04)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:8.

1)-2 Production of Inner Layer

To the above prepared lanthanum containing theta-alumina supporting theperovskite-type composite oxide was added the powdery lanthanumcontaining theta-alumina (Production Example C3) containing 4.0% byweight of lanthanum. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 75 g of the lanthanum containing theta-aluminasupporting the perovskite-type composite oxide and 90 g of the lanthanumcontaining theta-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an innerlayer.

2) Formation of Outer Layer

2)-1 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 38.6 g (0.095 mol) Ironethoxyethylate 18.4 g (0.057 mol) Manganese ethoxyethylate  8.9 g (0.038mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.04 g (0.005 mol) of silveracetylacetonate and 1.965 g (0.005 mol) of platinum acetylacetonate weredissolved in 200 mL of toluene, and the resulting solution was added tothe mixed alkoxide solution in the round bottomed flask to obtain aLaAgFeMnPt containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production ExampleA10) comprising a Zr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05) oxide wasdispersed in 200 mL of toluene and the homogeneous mixed solution in theround bottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaAgFeMnPtcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyzirconia composite oxide comprising aZr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05) oxide supporting aLa_(0.95)Ag_(0.05)Fe_(0.57)Mn_(0.38)Pt_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the powdery zirconia composite oxide supporting the perovskite-typecomposite oxide were added the powdery Rh supporting zirconia compositeoxide (Production Example A1-1) comprising aZr_(0.79)Ce_(0.16)La_(0.01)Nd_(0.04) oxide supporting 0.50% by weight ofRh, the powdery Pt supporting ceria composite oxide (Production ExampleB1-6) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.10% byweight of Pt and the powdery Pt—Rh supporting gamma-alumina (ProductionExample C10-1) comprising lanthanum containing gamma-alumina (lanthanumcontent: 4.0% by weight) supporting 0.33% by weight of Pt and 0.25% byweight of Rh. The resulting mixture was further mixed with deionizedwater and then mixed with alumina sol to form a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm thereby tohomogeneously apply, to a surface of the inner layer, 50 g of thezirconia composite oxide supporting the perovskite-type composite oxide,30 g of the Rh supporting zirconia composite oxide, 60 g of the Ptsupporting ceria composite oxide, and 60 g of the Pt—Rh supportinglanthanum containing gamma-alumina per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an outer layer. Thus, an exhaust gas purifying catalyst wasproduced.

The resulting exhaust gas purifying catalyst contained 0.65 g of Pt,0.26 g of Pd, and 0.30 g of Rh per one liter of the honeycomb carrier.

Example RC-11

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

1)-2 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol)Strontium ethoxyethylate  2.7 g (0.010 mol) Iron ethoxyethylate 18.4 g(0.057 mol) Manganese ethoxyethylate  8.9 g (0.038 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 11.48 g (corresponding to 0.975 g (0.005mol) of Pt) of a dinitrodiammine platinum nitrate solution having a Ptcontent of 8.50% by mass was dissolved in 100 mL of toluene, and theresulting solution was added to the mixed alkoxide solution in the roundbottomed flask to obtain a LaSrFeMnPt containing homogeneous mixedsolution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a powdery lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaSrFeMnPt composite oxide. Next, the lanthanumcontaining theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery lanthanumcontaining theta-alumina supporting aLa_(0.90)Sr_(0.10)Fe_(0.57)Mn_(0.38)Pt_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

1)-3 Production of Inner Layer

To the above prepared powdery lanthanum containing theta-aluminasupporting the palladium containing perovskite-type composite oxide andthe powdery lanthanum containing theta-alumina supporting the platinumcontaining perovskite-type composite oxide were added the powderylanthanum containing gamma-alumina (Production Example C10) containing4.0% by weight of lanthanum and the powdery BaSO₄. The resulting mixturewas further mixed with deionized water and then mixed with alumina solto form a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 3 mil per 600 cells, a diameter of 86 mm and alength of 104 mm so as to homogeneously apply 24 g of the lanthanumcontaining theta-alumina supporting the palladium containingperovskite-type composite oxide, 20 g of the lanthanum containingtheta-alumina supporting the platinum containing perovskite-typecomposite oxide, 40 g of the lanthanum containing gamma-alumina, and 20g of BaSO₄ per one liter of the honeycomb carrier. The resulting articledried at 100° C. and baked at 500° C. to form an inner layer.

2) Formation of Outer Layer

2)-1 Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 24.6 g (0.076 mol) Manganese ethoxyethylate  4.4 g (0.019mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 200 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeMnRh containing homogeneous mixed solution.

Separately, the powdery SrZrO₃ (Production Example D1) was dispersed in200 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain SrZrO₃ with adispersed pre-crystallization composition of a LaFeMnRh composite oxide.Next, SrZrO₃ with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain SrZrO₃ supporting aLa_(1.00)Fe_(0.76)Mn_(0.19)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to SrZrO₃ of 1:2.

The powdery SrZrO₃ supporting the rhodium containing perovskite-typecomposite oxide was impregnated with a dinitrodiammine platinum nitratesolution, dried at 100° C. and baked at 500° C. to obtain SrZrO₃supporting a Pt supporting rhodium containing perovskite-type compositeoxide. The amount of Pt supported of the SrZrO₃ supporting the Ptsupporting rhodium containing perovskite-type composite oxide was 1.33%by weight based on the rhodium containing perovskite-type compositeoxide.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery SrZrO₃ supporting the Pt supportingrhodium containing perovskite-type composite oxide were added thepowdery Pt supporting ceria composite oxide (Production Example B1-2)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weightof Pt and the powdery lanthanum containing gamma-alumina (ProductionExample C10) containing 4.0% by weight of lanthanum. The resultingmixture was further mixed with deionized water and then mixed withalumina sol to form a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm thereby to homogeneously apply, to asurface of the inner layer, 45 g of the SrZrO₃ supporting the Ptsupporting rhodium containing perovskite-type composite oxide, 20 g ofthe Pt supporting ceria composite oxide, and 50 g of the lanthanumcontaining gamma-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an outerlayer. Thus, an exhaust gas purifying catalyst was produced.

The exhaust gas purifying catalyst contained 0.70 g of Pt, 0.26 g of Pd,and 0.32 g of Rh per one liter of the honeycomb carrier.

Example RC-12

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:8.

1)-2 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol)Calcium ethoxyethylate  2.2 g (0.010 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of platinumacetylacetonate was dissolved in 200 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production ExampleA11) comprising a Zr_(0.60)Ce_(0.30)La_(0.05)Nd_(0.05) oxide wasdispersed in 200 mL of toluene and the homogeneous mixed solution in theround bottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a powdery zirconiacomposite oxide with a dispersed pre-crystallization composition of aLaCaFePt composite oxide. Next, the zirconia composite oxide with thedispersed pre-crystallization composition was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 650° C. in the air for one hour toobtain a powdery zirconia composite oxide comprising aZr_(0.60)Ce_(0.30)La_(0.05)Nd_(0.05) oxide supporting aLa_(0.90)Ca_(0.10)Fe_(0.95)Pt_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

1)-3 Production of Inner Layer

To the above prepared powdery lanthanum containing theta-aluminasupporting the palladium containing perovskite-type composite oxide andthe powdery zirconia composite oxide supporting the platinum containingperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B1-2) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weight of Pt andthe powdery lanthanum containing theta-alumina (Production Example C3)containing 4.0% by weight of lanthanum. The resulting mixture wasfurther mixed with deionized water and then mixed with alumina sol toform a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 3 mil per 600 cells, a diameter of 86 mm and alength of 104 mm so as to homogeneously apply 60 g of the lanthanumcontaining theta-alumina supporting the palladium containingperovskite-type composite oxide, 30 g of the zirconia composite oxidesupporting the platinum containing perovskite-type composite oxide, 20 gof the Pt supporting ceria composite oxide, and 40 g of the lanthanumcontaining theta-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an innerlayer.

2) Formation of Outer Layer

2)-1 Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Aluminumethoxyethylate 16.8 g (0.057 mol) Manganese ethoxyethylate  8.9 g (0.038mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaAlMnRh containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaAlMnRh composite oxide. Next, the lanthanumcontaining theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery lanthanumcontaining theta-alumina supporting aLa_(1.00)Al_(0.57)Mn_(0.38)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:2.

2)-2 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 36.6 g (0.090 mol)Calcium ethoxyethylate  2.2 g (0.010 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 500 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of platinumacetylacetonate was dissolved in 200 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

A powdery zirconia composite oxide (Production Example A11) comprising aZr_(0.60)Ce_(0.30)La_(0.05)Nd_(0.05) oxide was dispersed in 200 mL oftoluene and the homogeneous mixed solution in the round bottomed flaskwas added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaCaFePtcomposite oxide. Next, the powdery zirconia composite oxide with thedispersed pre-crystallization composition was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 650° C. in the air for one hour toobtain a powdery zirconia composite oxide comprisingZr_(0.60)Ce_(0.30)La_(0.05)Nd_(0.05) oxide supporting aLa_(0.90)Ca_(0.10)Fe_(0.95)Pt_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:8.

2)-3 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery lanthanum containing theta-aluminasupporting the rhodium containing perovskite-type composite oxide andthe powdery zirconia composite oxide supporting the platinum containingperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B1-2) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.50% by weight of Pt andthe powdery lanthanum containing theta-alumina (Production Example C3)containing 4.0% by weight of lanthanum. The resulting mixture wasfurther mixed with deionized water and then mixed with alumina sol toform a slurry. The slurry was injected into a honeycomb cordieritecarrier having a size of 3 mil per 600 cells, a diameter of 86 mm and alength of 104 mm thereby to homogeneously apply, to a surface of theinner layer, 45 g of the lanthanum containing theta-alumina supportingthe rhodium containing perovskite-type composite oxide, 30 g of thezirconia composite oxide supporting the platinum containingperovskite-type composite oxide, 40 g of the Pt supporting ceriacomposite oxide, and 30 g of the lanthanum containing theta-alumina perone liter of the honeycomb carrier. The resulting article dried at 100°C. and baked at 500° C. to form an outer layer. Thus, an exhaust gaspurifying catalyst was produced.

The resulting exhaust gas purifying catalyst contained 0.78 g of Pt,0.26 g of Pd, and 0.34 g of Rh per one liter of the honeycomb carrier.

Example RC-13

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

A powdery lanthanum containing theta-alumina (Production Example C3)containing 4.0% by weight of lanthanum was dispersed in 200 mL oftoluene and the homogeneous mixed solution in the round bottomed flaskwas added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, to obtain a lanthanumcontaining theta-alumina with a diepersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

1)-2 Production of Inner Layer

To the above prepared lanthanum containing theta-alumina supporting thepalladium containing perovskite-type composite oxide were added thepowdery Pt supporting ceria composite oxide (Production Example B1-7)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weightof Pt and the powdery theta-alumina. The resulting mixture was furthermixed with deionized water and then mixed with alumina sol to form aslurry. The slurry was injected into a honeycomb cordierite carrierhaving a size of 3 mil per 600 cells, a diameter of 86 mm and a lengthof 104 mm so as to homogeneously apply 28 g of the lanthanum containingtheta-alumina supporting the palladium containing perovskite-typecomposite oxide, 60 g of the Pt supporting ceria composite oxide, and 70g of the theta-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an innerlayer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting zirconia composite oxide (ProductionExample A6-4) comprising a Zr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxidesupporting 0.27% by weight of Pt and 1.33% by weight of Rh, the powderyPt supporting ceria composite oxide (Production Example B1-7) comprisinga Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt andthe powdery Pt supporting theta-alumina (Production Example C6)comprising a theta-alumina supporting 0.31% by weight of Pt were mixed.The resulting mixture was further mixed with deionized water and thenmixed with alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm thereby to homogeneously apply,to a surface of the inner layer, 30 g of the Pt—Rh supporting zirconiacomposite oxide, 60 g of the Pt supporting ceria composite oxide, and 70g of the Pt supporting theta-alumina per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an outer layer. Thus, an exhaust gas purifying catalyst wasproduced.

The exhaust gas purifying catalyst contained 0.10 g of Pt and 0.30 g ofPd in the inner layer, and 0.50 g of Pt and 0.40 g of Rh in the outerlayer, respectively, per one liter of the honeycomb carrier.

Example RC-14

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (ProductionExample C3) containing 4.0% by weight of lanthanum was dispersed in 200mL of toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, to obtain a lanthanumcontaining theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

1)-2 Production of Inner Layer

To the above prepared lanthanum containing theta-alumina supporting thepalladium containing perovskite-type composite oxide were added thepowdery Pt supporting ceria composite oxide (Production Example B1-8)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.67% by weightof Pt and the powdery theta-alumina. The resulting mixture was furthermixed with deionized water and then mixed with alumina sol to form aslurry. The slurry was injected into a honeycomb cordierite carrierhaving a size of 3 mil per 600 cells, a diameter of 86 mm and a lengthof 104 mm so as to homogeneously apply 30 g of the lanthanum containingtheta-alumina supporting the palladium containing perovskite-typecomposite oxide, 30 g of the Pt supporting ceria composite oxide, and 80g of the theta-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an innerlayer.

2) Production of outer layer and exhaust gas purifying catalyst Thepowdery Pt—Rh supporting zirconia composite oxide (Production ExampleA3-1) comprising a Zr_(0.50)Ce_(0.40)La_(0.05)Nd_(0.05) oxide supporting0.27% by weight of Pt and 1.33% by weight of Rh, the powdery Ptsupporting ceria composite oxide (Production Example B1-7) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt andthe powdery Pt—Rh supporting theta-alumina (Production Example C8-5)comprising theta-alumina supporting 0.43% by weight of Pt and 0.21% byweight of Rh were mixed. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm therebyto homogeneously apply, to a surface of the inner layer, 30 g of thePt—Rh supporting zirconia composite oxide, 60 g of the Pt supportingceria composite oxide, and 70 g of the Pt—Rh supporting theta-aluminaper one liter of the honeycomb carrier. The resulting article dried at100° C. and baked at 500° C. to form an outer layer. Thus, an exhaustgas purifying catalyst was produced.

The exhaust gas purifying catalyst contained 0.20 g of Pt and 0.33 g ofPd in the inner layer, and 0.58 g of Pt and 0.55 g of Rh in the outerlayer, respectively, per one liter of the honeycomb carrier.

Example RC-15

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery barium containing theta-alumina (ProductionExample C5) containing 4.0% by weight of barium was dispersed in 200 mLof toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, to obtain a barium containingtheta-alumina with a dispersed pre-crystallization composition of aLaFePd composite oxide. Next, the barium containing theta-alumina withthe dispersed pre-crystallization composition was placed on a petridish, subjected to forced air drying at 60° C. for twenty four hours andheat treated in an electric furnace at 650° C. in the air for one hourto obtain a powdery barium containing theta-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the barium containing theta-aluminaof 1:4.

1)-2 Production of Inner Layer

To the above prepared barium containing theta-alumina supporting thepalladium containing perovskite-type composite oxide was added thepowdery Pt supporting ceria composite oxide (Production Example B1-8)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.67% by weightof Pt. The resulting mixture was further mixed with deionized water andthen mixed with alumina sol to form a slurry. The slurry was injectedinto a honeycomb cordierite carrier having a size of 3 mil per 600cells, a diameter of 86 mm and a length of 104 mm so as to homogeneouslyapply 46 g of the barium containing theta-alumina supporting thepalladium containing perovskite-type composite oxide and 45 g of the Ptsupporting ceria composite oxide per one liter of the honeycomb carrier.The resulting article dried at 100° C. and baked at 500° C. to form aninner layer.

2) Formation of Outer Layer

2)-1 Supporting of Rhodium Containing Perovskite-Type Composite Oxide byThermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a theta-alumina witha dispersed pre-crystallization composition of a LaFeRh composite oxide.Next, the theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery theta-aluminasupporting a La_(1.00)Fe_(0.95)Rh_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:3.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery theta-alumina supporting the rhodiumcontaining perovskite-type composite oxide was added the powdery Ptsupporting ceria composite oxide (Production Example B1-8) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.67% by weight of Pt. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm thereby to homogeneously apply,to a surface of the inner layer, 38 g of the theta-alumina supportingthe rhodium containing perovskite-type composite oxide and 60 g of thePt supporting ceria composite oxide per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an outer layer. Thus, an exhaust gas purifying catalyst wasproduced.

The exhaust gas purifying catalyst contained 0.30 g of Pt and 0.20 g ofPd in the inner layer, and 0.40 g of Pt and 0.20 g of Rh in the outerlayer, respectively, per one liter of the honeycomb carrier.

Example RC-16

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum methoxypropylate 40.6 g (0.100 mol) Ironmethoxypropylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. Then, a brown viscous precipitate was formed uponhydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, to obtain a theta-aluminawith a dispersed pre-crystallization composition of a LaFePd compositeoxide. Next, the theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery theta-aluminasupporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:3.

1)-2 Production of Inner Layer

To the above prepared theta-alumina supporting the palladium containingperovskite-type composite oxide were added the powdery Pt supportingceria composite oxide (Production Example B1-7) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt andthe powdery theta-alumina. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 40 g of the theta-alumina supporting the palladiumcontaining perovskite-type composite oxide, 30 g of the Pt supportingceria composite oxide, and 80 g of the theta-alumina per one liter ofthe honeycomb carrier. The resulting article dried at 100° C. and bakedat 500° C. to form an inner layer.

2) Formation of Outer Layer

2)-1 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum methoxypropylate 38.6 g (0.090 mol)Calcium methoxypropylate  2.2 g (0.010 mol) Iron methoxypropylate 29.1 g(0.090 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate was dissolved in 40 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the solution overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a theta-alumina witha dispersed pre-crystallization composition of a LaCaFePt compositeoxide. Next, the theta-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery theta-aluminasupporting a La_(0.90)Ca_(0.10)Fe_(0.90)Pt_(0.10)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 2:3.

2)-2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery theta-alumina supporting the platinumcontaining perovskite-type composite oxide were added the powdery Pt—Rhsupporting zirconia composite oxide (Production Example A12-1)comprising a Zr_(0.70)Ce_(0.25)La_(0.02)Nd_(0.03) oxide supporting 0.75%by weight of Pt and 1.25% by weight of Rh and the powdery Pt supportingceria composite oxide (Production Example B1-7) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm thereby to homogeneously apply,to a surface of the inner layer, 3.2 g of the theta-alumina supportingthe platinum containing perovskite-type composite oxide, 40 g of thePt—Rh supporting zirconia composite oxide, and 60 g of the Pt supportingceria composite oxide per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an outerlayer. Thus, an exhaust gas purifying catalyst was produced.

The resulting exhaust gas purifying catalyst contained 0.10 g of Pt and0.35 g of Pd in the inner layer, and 0.60 g of Pt and 0.50 g of Rh inthe outer layer, respectively, per one liter of the honeycomb carrier.

Comparative Example PX-1

The powdery Pd supporting gamma-alumina (Production Example C11-2)comprising gamma-alumina supporting 1.63% by weight of Pd was mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of6 mil per 400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 200 g of the Pd supporting gamma-alumina per oneliter of the honeycomb carrier. The resulting article was dried at 100°C. and baked at 500° C. to obtain an exhaust gas purifying catalyst. Theresulting exhaust gas purifying catalyst contained 3.26 g of Pd per oneliter of the honeycomb carrier.

Comparative Example PX-2

The powdery Rh supporting gamma-alumina (Production Example C12)comprising gamma-alumina supporting 1.58% by weight of Rh was mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of6 mil per 400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 200 g of the Rh supporting gamma-alumina per oneliter of the honeycomb carrier. The resulting article was dried at 100°C. and baked at 500° C. to obtain an exhaust gas purifying catalyst. Theresulting exhaust gas purifying catalyst contained 3.16 g of Rh per oneliter of the honeycomb carrier.

Comparative Example PX-3

To the powdery Pt—Rh supporting gamma-alumina (Production Example C13-2)comprising gamma-alumina supporting 2.00% by weight of Pt and 0.20% byweight of Rh was added the powdery Pt supporting ceria composite oxide(Production Example B3-3) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxidesupporting 0.10% by weight of Pt. The resulting mixture was mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of6 mil per 400 cells, a diameter of 80 mm and a length of 95 mm so as tohomogeneously apply 100 g of the Pt—Rh supporting gamma-alumina and 40 gof the Pt supporting ceria composite oxide per one liter of thehoneycomb carrier. The resulting article was dried at 100° C. and bakedat 500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 2.4 g of Pt and 0.20 g of Pdper one liter of the honeycomb carrier. Comparative Example QX-5Lanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production ExampleA13) comprising a Zr_(0.70)Ce_(0.25)La_(0.02)Y_(0.03) oxide wasdispersed in 200 mL of toluene and the homogeneous mixed solution in theround bottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFePdcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyexhaust gas purifying catalyst comprising aZr_(0.70)Ce_(0.25)La_(0.02)Y_(0.03) oxide zirconia composite oxidesupporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 1:4.Comparative Example QX-6 Lanthanum ethoxyethylate 40.6 g (0.100 mol)Iron ethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production ExampleA10) comprising a Zr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05) oxide wasdispersed in 100 mL of toluene and the homogeneous mixed solution in theround bottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a zirconia compositeoxide with a dispersed pre-crystallization composition of a LaFeRhcomposite oxide. Next, the zirconia composite oxide with the dispersedpre-crystallization composition was placed on a petri dish, subjected toforced air drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyexhaust gas purifying catalyst comprising aZr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05) oxide zirconia composite oxidesupporting a La_(1.00)Fe_(0.95)Rh_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:3.Comparative Example QX-7 Lanthanum methoxypropylate 36.6 g (0.090 mol)Calcium methoxypropylate  2.2 g (0.010 mol) Iron methoxypropylate 29.1 g(0.090 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production ExampleA14) comprising a Zr_(0.70)Ce_(0.25)Pr_(0.02)Nd_(0.03) oxide wasdispersed in 100 mL of toluene and the homogeneous mixed solution in theround bottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, to obtain a zirconiacomposite oxide with a dispersed pre-crystallization composition of aLaCaFePt containing perovskite-type composite oxide. Next, the zirconiacomposite oxide with the dispersed pre-crystallization composition wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 800° C. inthe air for one hour to obtain a powdery exhaust gas purifying catalystcomprising a Zr_(0.70)Ce_(0.25)Pr_(0.02)Nd_(0.03) oxide zirconiacomposite oxide supporting a La_(0.90)Ca_(0.10)Fe_(0.90)Pt_(0.10)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 1:4.Comparative Example QX-8 Lanthanum ethoxyethylate 40.6 g (0.100 mol)Iron ethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery gamma-alumina was dispersed in 100 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a gamma-alumina witha dispersed pre-crystallization composition of a LaFePd composite oxide.Next, the gamma-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery exhaust gaspurifying catalyst comprising a gamma-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the gamma-alumina of 1:4.

Comparative Example RX-9

The powdery Pd supporting gamma-alumina (Production Example C11-3)supporting 0.44% by weight of Pd was mixed with deionized water and thenmixed with alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 80 mm and a length of 104 mm so as to homogeneously apply150 g of the Pd supporting gamma-alumina per one liter of the honeycombcarrier. The resulting article was dried at 100° C. and baked at 500° C.to obtain an exhaust gas purifying catalyst. The resulting exhaust gaspurifying catalyst contained 0.66 g of Pd per one liter of the honeycombcarrier.

Comparative Example RX-10

To the powdery Pt—Rh supporting gamma-alumina (Production Example C13-3)comprising gamma-alumina supporting 0.67% by weight of Pd and 0.42% byweight of Rh was added the powdery Pt supporting ceria composite oxide(Production Example B3-4) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxidesupporting 0.67% by weight of Pt. The resulting mixture was mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 80 mm and a length of 104 mm so as tohomogeneously apply 150 g of the Pt—Rh supporting gamma-alumina and 75 gof the Pt supporting ceria composite oxide per one liter of thehoneycomb carrier. The resulting article was dried at 100° C. and bakedat 500° C. to obtain an exhaust gas purifying catalyst. The resultingexhaust gas purifying catalyst contained 1.50 g of Pt and 0.63 g of Rhper one liter of the honeycomb carrier.

Comparative Example RX-11

To the powdery Pd supporting theta-alumina (Production Example C9-2)comprising theta-alumina supporting 1.10% by weight of Pd were added thepowdery Pt supporting ceria composite oxide (Production Example B1-10)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 1.50% by weightof Pt and the powdery Pt—Rh supporting theta-alumina (Production ExampleC8-7) comprising theta-alumina supporting 1.50% by weight of Pt and0.67% by weight of Rh. The resulting mixture was mixed with deionizedwater and then mixed with alumina sol to form a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 30 g of the Pd supporting theta-alumina, 40 g of thePt supporting ceria composite oxide and 60 g of the Pt—Rh supportingtheta-alumina per one liter of the honeycomb carrier. The resultingarticle was dried at 100° C. and baked at 500° C. to obtain an exhaustgas purifying catalyst. The resulting exhaust gas purifying catalystcontained 1.50 g of Pt, 0.33 g of Pd, and 0.40 g of Rh per one liter ofthe honeycomb carrier.

Comparative Example RX-12

1) Formation of Inner Layer

To the powdery Pd supporting ceria composite oxide (Production ExampleB4-1) comprising Ce_(0.80)Zr_(0.20)O₂ supporting 3.30% by weight of Pdwere added the powdery gamma-alumina and the powdery BaSO₄. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply 45g of the Pd supporting ceria composite oxide, 50 g of the gamma-alumina,and 20 g of BaSO₄ per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting ceria composite oxide (Production ExampleB5-1) comprising Ce_(0.30)Zr_(0.70)O₂ supporting 2.00% by weight of Ptand 1.70% by weight of Rh and the powdery gamma-alumina were mixed. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was injected into thehoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply,to a surface of the inner layer, 75 g of the Pt—Rh supporting ceriacomposite oxide and 75 g of the gamma-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an outer layer. Thus, an exhaust gas purifying catalystwas produced.

The resulting exhaust gas purifying catalyst contained 1.50 g of Pd inthe inner layer, and 1.50 g of Pt and 1.30 g of Rh in the outer layer,respectively, per one liter of the honeycomb carrier.

Comparative Example RX-13

1) Formation of Inner Layer

1)-1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide Lanthanum ethoxyethylate 40.6 g (0.100 mol) Ironethoxyethylate 30.7 g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask and dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, and the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery gamma-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a gamma-alumina witha dispersed pre-crystallization composition of a LaFePd composite oxide.Next, the gamma-alumina with the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 650° C. in the air for one hour to obtain a powdery gamma-aluminasupporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the gamma-alumina of 1:1.

1)-2 Production of Inner Layer

To the above prepared powdery gamma-alumina supporting the palladiumcontaining perovskite-type composite oxide was added a powderygamma-alumina. The resulting mixture was further mixed with deionizedwater and then mixed with alumina sol to form a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 60 g of the gamma-alumina supporting the palladiumcontaining perovskite-type composite oxide and 30 g of the gamma-aluminaper one liter of the honeycomb carrier. The resulting article dried at100° C. and baked at 500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the powdery Pt—Rh supporting ceria composite oxide (ProductionExample B5-2) comprising Ce_(0.30)Zr_(0.70)O₂ supporting 2.00% by weightof Pt and 1.00% by weight of Rh was added the powdery gamma-alumina. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply,to a surface of the inner layer, 50 g of the Pt—Rh supporting ceriacomposite oxide and 30 g of the gamma-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an outer layer. Thus, an exhaust gas purifying catalystwas produced.

The resulting exhaust gas purifying catalyst contained 1.00 g of Pt,0.66 g of Pd, and 0.50 g of Rh per one liter of the honeycomb carrier.

Measurement

Test Example 1

1) Endurance Test

The exhaust gas purifying catalysts of examples and comparative examplesshown in Table 1 were connected to both banks of a V type eight cylinderengine having a displacement of 4 liters and were subjected to anendurance test at a temperature in the catalyst bed of 900° C. with asingle cycle of 900 seconds repeated for the time shown in Table 1.

One cycle of the endurance test was set as follows. Specifically, fromSecond 0 to Second 870 (a period of 870 seconds), an oscillation(amplitude) of Δλ=±4% (ΔA/F=±0.6 A/F) of which the center was set in thetheoretical fuel-air ratio of A/F=14.6 (λ=1) (A/F=air to fuel ratio) wasapplied to the monolith catalysts at a frequency of 0.6 Hz. From Second870 to Second 900 (a period of 30 seconds), secondary air was introducedupstream of the catalysts to achieve forced oxidation under theconditions (λ=1.25).

2) Activity Determination (Purification Rates of CO, HC, and NOx)

Using a model gas shown in Table 2, activity of test pieces having adiameter of 80 mm and a length of 95 mm (test pieces sampled from theexhaust gas purifying catalysts of examples and comparative examplesafter the endurance test) was determined by a sweep test.

In the sweep test, an oscillation (amplitude) of Δλ=3.4% (ΔA/F=±0.5 A/F)of which the center was set in the theoretical fuel-air ratio (λ=1) wasapplied to the test pieces at a frequency of 0.5 Hz. The purificationrates of CO, HC, and NOx of the test pieces were measured. The resultsare shown in Table 1. In the measurement, the upstream (inlet gas) ofthe monolith catalysts was kept at 400° C., and the flow rate was set ata space velocity shown in Table 1. TABLE 1 Test Example 1 Activitydetermination Endurance (purification rates of CO, Examples/ Amountsupported test HC, and NOx) Comparative (g/L) Cycling Space CO HC NOxExamples Composition Pt Pd Rh time (hrs) velocity (%) (%) (%) ExampleLa1.00Fe0.57Mn0.38Pd0.05O3 (150 g) + theta- — 3.26 — 100 SV35000 97.799.8 97.7 PA-1 alumina (50 g) (3:1) Example La1.00Fe0.95Pd0.05O3/ — 3.26— 100 SV35000 98.0 99.8 97.8 PA-2 theta-alumina (3:1) (200 g) ExampleLa1.00Fe0.57Mn0.38Rh0.05O3 (150 g) + theta- — — 3.15 120 SV40000 93.994.7 94.4 PA-3 alumina (50 g) (3:1) ExampleLa0.80Pr0.20Fe0.75Ti0.20Rh0.05O3/ — — 3.16 120 SV40000 94.1 95.8 95.6PA-4 theta-alumina (3:1) (200 g) Example Pt/La1.00Fe0.95Rh0.05O3 (150g) + theta- 1.50 — 3.15 120 SV40000 95.3 97.7 96.6 PA-5 alumina (50 g)(3:1) Example La0.90Sr0.10Fe0.57Mn0.3BPt0.05O3 (60 g) + theta- 2.39 — —120 SV40000 85.2 88.7 85.4 PA-6 alumina (50 g) ExampleLa0.95Ag0.05A10.85Mn0.10Pt0.05O3 (54 g)/ 2.41 — — 120 SV40000 87.1 89.285.2 PA-7 theta-alumina (50 g) ExampleNd0.80Ba0.10Mg0.10A10.85Pt0.10Rh0.05O3 2.41 — 0.66 120 SV40000 93.2 93.791.8 PA-8 (28 g) + theta- alumina (50 g) ExampleLa0.90Sr0.10Fe0.57Mn0.38Pt0.05O3 (60 g) + 2.39 — 0.19 120 SV40000 94.192.3 91.4 PA-9 La1.00Fe0.57Mn0.38Rh0.05O3 (9 g) + La- theta-alumina (La:4%) (100 g) Example La1.00Fe0.95Pd0.05O3 (138 g) + — 2.41 0.19 120SV40000 94.4 93.2 95.1 PA-10 La1.00Fe0.95Rh0.05O3 (9 g) +La-theta-alumina (La: 4%) (100 g) Example La1.00Fe0.95Pd0.05O3 (92 g) +0.50 2.00 0.20 120 SV40000 95.1 94.2 93.4 PA-11La0.95Ag0.05A10.85Mn0.10Pt0.05O3 (11.2 g) + Rh/Zr0.79Ce0.16La0.01Nd0.04Oxide (40 g) + La- theta-alumina (La: 4%) (100 g) ComparativePd/gamma-alumina (200 g) — 3.26 — 100 SV35000 87.2 99.4 97.2 ExamplePX-1 Comparative Rh/gamma-alumina (200 g) — — 3.16 120 SV40000 85.2 83.684.3 Example PX-2 Comparative Pt-Rh/gamma-alumina (100 g) +Pt/Ce0.60Zr0.30Y0.10 2.40 — 0.20 120 SV40000 76.2 79.6 74.3 ExampleOxide (40 g) PX-3

TABLE 2 Gas CO H₂ C₃H₆ C₃H₈ O₂ NOx CO₂ Reducing side 22000 7333 500 1336700 1700 80000 (λ = 0.966) Theoretical 7000 2333 ↑ ↑ 6700 ↑ ↑ fuel-airratio (λ = 1.000) Oxidation side 7000 2333 ↑ ↑ 16700 ↑ ↑ (λ = 1.034)

Test Example 2

1) High Temperature Endurance Treatment (R/L 1000° C.)

The above prepared powdery exhaust gas purifying catalysts according toExamples and Comparative Examples shown in Table 3 were subjected tohigh temperature endurance treatment under the following conditions. Inthe high temperature endurance treatment, the atmospheric temperaturewas set at 1000° C., and a cycle for a total of 30 minutes comprising aninert atmosphere for 5 minutes, an oxidative atmosphere for 10 minutes,an inert atmosphere for 5 minutes, and a reducing atmosphere for 10minutes was repeated 10 times, for a total of five hours. The aboveatmospheres were constituted by supplying gases containing hightemperature steam and having the following gas compositions,respectively, at a flow rate of 300 L/hr. The temperatures of theatmospheres were hold to 1000° C. by the action of high temperaturesteam.

-   -   Inert atmosphere gas composition: 8% of CO₂, 10% of H₂O, with        the balance of N₂    -   Oxidative atmosphere gas composition: 1% of O₂, 8% of CO₂, 10%        of H₂O, with the balance of N₂    -   Reducing atmosphere gas composition: 0.5% of H₂, 1.5% of CO, 8%        of CO₂, 10% of H₂O, with the balance of N₂        2) High Temperature Endurance Treatment (Air 1150° C.)

The above prepared powdery exhaust gas purifying catalysts according toExamples and Comparative Examples shown in Table 3 were subjected to thehigh temperature endurance treatment in an atmosphere of the air (in anormal atmosphere).

3) Measurement of Specific Surface Area

The specific surface areas of the above prepared powdery exhaust gaspurifying catalysts according to Examples and Comparative Examples shownin Table 3 were determined before and after the high temperatureendurance treatments. The specific surface areas were measured accordingto the BET method. The results are shown in Table 3. TABLE 3 TestExample 2 Specific surface area (m2/g) After After endurance enduranceBefore high After treatment/Before After treatment/Before Examples/temperature endurance endurance endurance endurance Comparativeendurance treatment treatment treatment treatment Examples Compositiontreatment (1000° C.) (1000° C.) (%) (1150° C.) (1150° C.) (%) ExampleLa1.00Fe0.90Pd0.10O3 + theta- 70.2 62.1 88.5 38.1 54.3 QA-12 alumina(1:2) Example La1.00Fe0.95Pd0.05O3/ 75.2 66.2 88.0 40.2 53.5 QA-13theta-alumina (1:3) Example La1.00Fe0.95Pd0.05O3/ 87.5 82.5 94.3 62.271.1 QA-14 La-theta-alumina (La: 4%) (1:4) Example La1.00Fe0.95Pd0.05O3/51.2 46.1 90.0 35.3 68.9 QA-15 La-theta-alumina (La: 4%) (1:1) ExampleLa1.00Fe0.57Mn0.38Rh0.05O3/ 96.4 91.3 94.7 71.9 74.6 QA-16La-theta-alumina (La: 2%) (1:9) Example La1.00Fe0.95Rh0.05O3/ 63.2 57.390.7 43.8 69.3 QA-17 La-theta-alumina (La: 10%) (2:3) ExampleLa0.95Ag0.05Fe0.57Mn0.38Pt0.05O3/ 51.1 47.2 92.4 35.5 69.5 QA-18La-theta-alumina (La: 10%) (1:1) Example La0.90Ca0.10Fe0.90Pt0.10O3/85.4 77.0 90.2 58.3 68.3 QA-19 theta-alumina (1:4) ComparativeLa1.00Fe0.95Pd0.05O3/ 50.1 42.3 84.4 5.3 10.6 ExampleZr0.70Ce0.25La0.02Y0.03 Oxide QX-5 (1:4) ComparativeLa1.00Fe0.95Rh0.05O3/ 25.2 16.0 63.5 3.4 13.5 ExampleZr0.50Ce0.40La0.05Y0.05 Oxide QX-6 (2:3) ComparativeLa0.90Ca0.10Fe0.90Pt0.10O3/ 43.2 35.3 81.7 3.1 7.2 ExampleZr0.70Ce0.25Pr0.02Nd0.03 Oxide QX-7 (1:4) ComparativeLa1.00Fe0.95Pd0.05O3/ 140.6 101.4 72.1 43.2 30.7 Example gamma-alumina(1:4) QX-8

Test Example 3

1) Endurance Test

The exhaust gas purifying catalysts according to Examples andComparative Examples were connected to a bank of a V type eight cylinderengine of 4 liters. With the cycle shown in Tables 4 to 7 as a singlecycle (30 seconds) at 1050° C. or 1100° C., the endurance test wasrepeated for time periods shown in Tables 4 to 7. Then, annealing wascarried out at a fuel-air ratio A/F of 14.3, at 900° C. for two hours.

One cycle was set as follows. Specifically, from Second 0 to Second 5 (aperiod of 5 seconds), a mixed gas which was kept of amount oftheoretical fuel-air ratio (A/F=14.6, in the stoichiometric state) underfeedback control was fed to the engine and the internal temperature ofthe exhaust gas purifying catalysts was set at around 850° C. FromSecond 5 to Second 30 (a period of 25 seconds), the feedback wasreleased. From Second 5 to Second 7 (a period of 2 seconds), the fuelwas injected excessively, so that the fuel rich mixed gas (A/F=11.2) wasfed to the engine. From Second 7 to Second 28 (a period of 21 seconds),while an excessive amount of fuel was kept on being fed to the engine,secondary air was introduced from the upstream into the exhaust gaspurifying catalysts through an inlet tube, to cause the excessive fuelto react with the secondary air in the interior of the exhaust gaspurifying catalysts, so as to raise the temperature. In this timeperiod, the fuel-air ratio in the exhaust gas in the exhaust gaspurifying catalysts was substantially kept in a somewhat lean state thanthe stoichiometric state (A/F=14.8), and the highest temperature in thecatalyst bed was 1050° C. or 1100° C. as shown in Tables 4 to 7. FromSecond 28 to Second 30 (a period of 2 seconds), no excessive fuel wasfed to the engine but the secondary air was fed to the exhaust gaspurifying catalysts to put the exhaust gas into a lean state.

The temperatures of the exhaust gas purifying catalysts were measuredwith a thermocouple inserted into a center part of the honeycombcarrier. A phosphorus compound was added to the fuel (gasoline) so thatphosphorus element in the exhaust gas poisons the catalysts. The amountof the phosphorus compound was set so that 816 mg in terms of phosphoruselement was deposited to the exhaust gas purifying catalysts during theendurance time shown in Tables 4 to 7.

2) HC 50% Purification Temperature

The mixed gas held substantially in the stoichiometric state wassupplied to the engine. While the temperature of the exhaust gasexhausted by the combustion of the mixed gas was raised at a rate of 30°C. per minute, the exhaust gas was fed to the exhaust gas purifyingcatalysts according to Examples and Comparative Examples shown in Tables4 to 7 which had been subjected to the endurance.

The exhaust gas was fed to the exhaust gas purifying catalysts at aspace velocity SV of 90000/h. The HC level in the exhaust gas treated bythe exhaust gas purifying catalysts was measured. In this procedure, theHC 50% purification temperature was defined as the temperature at thetime when HC in the exhaust gas was purified to 50%. The results areshown in Tables 4 to 7. The mixed gas to be fed to the engine was setsubstantially in the stoichiometric state by the feed back control, andthe A/F was set at 14.6±1.0.

3) Co—NOx Cross-Point Purification Rate

The mixed gas was fed to the engine, while it was varied from itsfuel-rich state to its lean state. The exhaust gas produced by thecombustion in the engine was purified by use of the exhaust gaspurifying catalysts of Examples and Comparative Examples shown in Tables4 and 6. The CO and NOx purifying rates were measured. A purifying rateobtained when the purifying rates of these components are coincidentwith each other was defined as a CO—NOx cross-point purifying rate. Theresults are shown in Tables 4 and 6. It is to be noted that themeasurement of the purifying rates was performed in the condition of theengine only, rather than in the condition in which the engine wasmounted on the automobile. The temperature of the exhaust gas fed to theexhaust gas purifying catalysts was set at 460° C. and space velocity SVwas set at 90000/h. TABLE 4 Test Example 3 HC 50% Endurance purificationExamples/ Amount supported test temperature Comparative (g/L) CyclingCO—NOx (° C.) Examples Composition Pt Pd Rh time (hrs) (%) 1050° C.Example La1.00Fe0.95Pd0.05O3/ — 0.66 — 48 72.0 400 RA-20Zr0.60Ce0.30La0.05Y0.05 Oxide (2:8) (150 g) + theta- alumina (1:1) (150g) Example La1.00Fe0.57Mn0.38Pd0.05O3/ 0.15 0.66 — 48 76.3 402 RA-21Zr0.50Ce0.40La0.05Nd0.05 Oxide (2:8) (150 g) + Pt/ Ce0.60Zr0.30Y0.10Oxide (60 g) + theta- alumina (90 g) Example La1.00Fe0.57Mn0.38Pd0.05O3/— 0.66 0.15 48 79.0 390 RA-22 Zr0.65Ce0.30La0.02Y0.03 Oxide (2:8) (150g) + Ce0.60Zr0.30Y0.10 Oxide (70 g) + Rh/ theta-alumina (80 g) ExampleLa1.00Fe0.95Pd0.05O3/ 0.30 0.66 0.15 48 81.0 378 RA-23Zr0.70Ce0.20La0.052Y0.05 Oxide (2:8) (150 g) + Pt-Rh/Zr0.76Ce0.18La0.02Nd0.04 Oxide (30 g) + Ce0.60Zr0.30Y0.10 Oxide (50g) + Pt- Rh/theta-alumina (60 g) Example La0.90Ce0.10Fe0.90Rh0.10O3/ — —0.63 48 79.2 392 RA-24 Zr0.60Ce0.30La0.05Y0.05 Oxide (1:9) (150 g) +theta- alumina (150 g) Example La0.90Ce0.10Fe0.95Rh0.05O3/ 0.30 — 0.6948 91.1 368 RA-25 La-theta-alumina (2:8) (La: 10%) (150 g) +Ce0.60Zr0.30Y0.10 Oxide (90 g) + Pt- Rh/theta-alumina (60 g) ExampleLa1.00Fe0.95Rh0.05/SrZrO3 (2:8) (150 g) + Pt- 0.45 — 0.78 48 94.0 353RA-26 Rh/Zr0.79Ce0.16La0.01Nd0.04 Oxide (60 g) + Pt/ Ce0.40Zr0.50Y0.10Oxide (30 g) + Pt- Rh/theta-alumina (60 g) ExampleLa0.90Ca0.10Fe0.90Pt0.10O3/ 0.59 — — 60 71.2 413 RA-27Zr0.60Ce0.30La0.05Y0.05 Oxide (1:9) (75 g) + theta- alumina (150 g)Example La0.90Ca0.10Fe0.95Pt0.05O3/ 0.91 — 0.10 60 86.1 388 RA-28La-theta-alumina (La: 10%) (2:8) (75 g) + Ce0.60Zr0.30Y0.10 Oxide (90g) + Pt- Rh/theta-alumina (60 g) Example La1.00Fe0.57Mn0.38Pd0.05O3/0.30 0.22 0.26 60 82.0 387 RA-29 Zr0.65Ce0.30La0.02Y0.03 Oxide (2:8) (50g) + La0.90Ce0.10Fe0.95Rh0.05O3/ La-theta-alumina (La: 4%) (2:8) (50g) + Pt/ Ce0.60Zr0.30Y0.10 Oxide (60 g) + theta- alumina (40 g) ExamplePd/La1.00Fe1.00O3 (30 g) + Pt- 0.58 0.66 0.12 60 83.2 385 RA-29-1Rh/Zr0.76Ce0.18La0.02Nd0.04 Oxide (40 g) + Pt/ Ce0.60Zr0.30Y0.10 Oxide(50 g) + theta- alumina (50 g) Comparative Pd/gamma-alumina (150 g) —0.66 — 48 60.3 445 Example RX-9 Comparative Pd-Rh/gamma-alumina (150g) + Pt/ 1.50 — 0.63 48 71.3 420 Example Ce0.60Zr0.30Y0.10 Oxide (75 g)RX-10

TABLE 5 Test Example 3 Endurance Amount supported test HC 50%purification (g/L) Cycling temperature (° C.) Examples Composition Pt PdRh time (hrs) 1050° C. 1100° C. Eample La1.00Fe0.95Pd0.05O3/ 1.50 0.330.40 40 — 392 RA-30 La-theta-alumina (La: 4%) (1:1) (30 g) + Pt- 48 351— Rh/zr0.76Ce0.18La0.02Nd0.04 Oxide (30 g) + Pt/Ce0.60Zr0.30Y0.10 Oxide(80 g) + Pt- Rh/theta-alumina (70 g) Example La1.00Fe0.95Pd0.05O3/ 1.500.33 0.40 40 — 423 RA-31 La-theta-alumina (La: 4%) (1:1) (30 g) +Pt/Ce0.60Zr0.30Y0.10 48 362 — Oxide (80 g) + Pt- Rh/gamma-alumina (70 g)Example La1.00Fe0.95Pd0.05O3 1.50 0.33 0.40 40 — 418 RA-32 alpha-alumina(1:2) (45 g) + Pt- 48 365 — Rh/Zr0.76Ce0.18La0.02Nd0.04 Oxide (40 g) +Pt/ Ce0.60Zr0.30Y0.10 Oxide (80 g) + gamma- alumina (70 g) ComparativePd/theta-alumina (30 g) + Pt/ 1.50 0.33 0.40 40 — >500   ExampleCe0.60Zr0.30Y0.10 Oxide (40 g) + Pt- 48 395 — RX-11 Rh/theta-alumina (60g)

TABLE 6 Test Example 3 En- durance HC 50% test purification AmountCycling temperature Composition supported (g/L) time CO—NOx (° C.)Examples Inner layer Outer layer Pt Pd Rh (hrs) (%) 1050° C. ExampleLa1.00Fe0.95Pd0.05O3/ PT-RH/Zr0.76Ce0.18La0.02Nd0.04 0.45 0.33 0.70 4883.3 374 RC-1 Zr0. 65Ce0.30La0.02Y0.03 Oxide Oxide (50 g) + Pt/ (2:8)(75 g) + Pt/ ce0.60zr0.30y0.10 Oxide Ce0.60Zr0.30Y0.10 Oxide (30 g) +theta- (50 g) + theta- alumina (50 g) alumina (70 g) ExampleLa1.00Fe0.95Pd0.05O3/SrZrO3 PT-RH/Zr0.76Ce0.18La0.02Nd0.04 0.45 0.330.70 48 84.0 371 RC-2 (2:8) (75 g) + Pt/ Oxide Ce0.60Zr0.30Y0.10 Oxide(50 g) + Pt/ (30 g) + theta- Ce0.60Zr0.30Y0.10 Oxide alumina (70 g) +BaSO4 (30 g) + theta- (20 g) alumina (50 g) Example La1.00Fe0.95Pd0.05O3PT-RH/Zr0.76Ce0.18La0.02Nd0.04 0.5 0.66 0.70 48 84.8 360 RC-3 (30 g) +Pt/ Oxide Ce0.60Zr0.30Y0.10 Oxide (50 g) + Pt/ (50 g) + theta-Ce0.60Zr0.30Y0.10 Oxide alumina (90 g) + BaSO4 (40%) + theta- (20 g)alumina (50 g) Example La1.00Fe0.95Pd0.05O3/PT-RH/zr0.80Ce0.15La0.02Nd0.03 0.78 0.33 0.55 48 87.3 358 RC-4Zr0.65Ce0.30La0.02Y0.03 Oxide Oxide (30 g) + Pt/ (2:8) (75 g) + Pt/Ce0.60Zr0.30Y0.10 Oxide Ce0.60Zr0.30Y0.10 Oxide (30 g) + Pt- (20 g) +theta- Rh/theta-alumina (70 g) alumina (90 g) ExampleLa1.00Fe0.96Pd0.04O3/theta- Rh/Zr0.80Ce0.15La0.02Nd0.03 0.70 0.26 0.4048 85.2 362 RC-5 alumina Oxide (2:8) (75 g) + Pt/ (30 g) + Pt/Ce0.60Zr0.30Y0.10 Oxide Ce0.60Zr0.30Y0.10 Oxide (20 g) + theta- (30 g) +Pt- alumina (90 g) Rh/theta-alumina (70 g) ExampleLa1.00Fe0.95Pd0.05O3/theta- La1.00Fe0.95Rh0.05O3/LaA1O3 0.40 0.80 0.4048 96.6 337 RC-6 alumina (2:8) (95 g) + Pt/ (50 g) + Ce0.60Zr0.30Y0.10Ce0.60Zr0.30Y0.10 Oxide Oxide (30 g) + theta- (30 g) + BaSO4 alumina (30g) (20 g) Example Pt/Ce0.40Zr0.50Y0.10 OxideLa0.90Sr0.10Fe0.90Pt0.05Rh0.05 0.74 0.20 0.40 60 90.8 371 RC-7 (30 g) +Pd/ O3/ theta-alumina (50 g) SrZrO3 (2:8) (75 g) + Pt-Rh/Zr0.79Ce0.16La0.01 Nd0.04 Oxide (60 g) Example Pd/gamma-alumina (50g) + La0.90Sr0.10Fe0.95Pt0.05O3/ 0.70 0.80 0.40 60 92.5 353 RC-8Ce0.60Zr0.30Y0.10 Oxide Zr0.60Ce0.30La0.05Y0.05 Oxide (30 g) + BasO4(2:8) (63 g) + Pt/ (20 g) Ce0.60Zr0.30Y0.10 Oxide (30 g) + Pt-Rh/theta-alumina (30 g) Example La1.00Fe0.95Pd0.05O3/La1.00Fe0.38A10.38Mn0.19Rh0.05 0.75 0.22 0.32 60 90.6 353 RC-9Zr0.65Ce0.30La0.02Y0.03 O3/ Oxide SrZrO3 (2:8) (50 g) + Pt- (2:8) (50g) + Pt/ Rh/La-theta-alumina Ce0.60Zr0.30Y0.10 Oxide (La: 4%) (60 g) (30g) + La- theta-alumina (La: 4%) (30 g) Example La1.00Fe0.96Pd0.4o3/La0.95Ag0.05Fe0.57Mn0.38Pt0.05o3/ 0.65 0.26 0.30 60 88.0 350 RC-10La-theta-alumina (La: 4%) Zr0.50Ce0.40La0.05Y0.05 Oxide (2:8) (75 g) +La- (2:8) (50 g) + Rh/ theta-alumina (La: 4%) Zr0.79Ce0.16La0.01Nd0.04(90 g) Oxide (30 g) + Pt/ Ce0.60Zr0.30Y0.10 Oxide (60 g) + Pt-Rh/La-gamma-alumina (La: 4% (60 g) Example La1.00Fe0.95Pd0.05o3/Pt/La1.00Fe0.76Mn0.19Rh0.05o3/ 0.70 0.26 0.32 60 90.8 346 RC-11La-theta-alumina (La: 4%) SrZrO3 (1:2) (45 g) + Pt/ (1:1) (24 g) +Ce0.60zr0.30Y0.10 Oxide La0.90Sr0.10Fe0.57Mn0.38Pt0.5o3/ (20 g) + La-La-theta-alumina (La: 4%) gamma-alumina (La: 4%) (50 g) (1:1) (20 g) +La- gamma-alumina (La: 4%) (40 g) + BaSO4 (20 g) ExampleLa1.00Fe0.95Pd0.05o3/ La1.00A10.57Mn0.38Rh0.05o3/ 0.78 0.26 0.34 60 91.3342 RC-12 La-theta-alumina (La: 4%) (2:8) La-theta-alumina (La: 4%) (60g) + La0.90Ca0.10Fe0.95Pt0.05o3/ (1:2) (45 g) + Zr0.60Ce0.30La0.05Nd0.05Oxide La0.90Ca0.10Fe0.95Pt0.05o3/ (2:8) (30 g) + Pt/Zr0.60Ce0.30La0.05Nd0.05 Oxide Ce0.60Zr0.30Y0.1 Oxide (20 g) + La- (2:8)(30 g) + Pt/ theta-alumina (La: 4%) (40 g) Ce0.60Zr0.30Y0.10 Oxide (40g) + La-theta-alumina (La: 4%) (30 g) Com- Pd/Ce0.80Zr0.20o2 (45 g) +gamma- Pt-Rh/Ce0.30Zr0.70o2 (75 g) + 1.50 1.50 1.30 48 82.0 375 parativealumina (50 g) + BaSO4 gamma-alumina (75 g) Example (20 g) RX-12

TABLE 7 Test Example 3 HC 50% Endurance purification Amount testtemperature Composition supported (g/L) Cycling time (° C.) EamplesInner layer Outer layer Pt Pd Rh (hrs) 1050° C. 1100° C. ExampleLa01.00Fe0.95Pd0.05o3/ Pt- 0.60 0.30 0.40 40 — 377 RC-13La-theta-alumina (La: 4%) Rh/Zr0.76Ce0.18La0.02Nd0.04 48 359 — (1:1) (28g) + Pt/ Oxide (30 g) + Pt/ Ce0.60Zr0.30Y0.10 Ce0.60Zr0.30Y0.10 Oxide(60 g) + theta- Oxide (60 g) + Pt/ alumina (70 g) theta-alumina (70 g)Example La01.00Fe0.95Pd0.05o3/ Pt- 0.78 0.33 0.55 40 — 368 RC-14La-theta-alumina (La: 4%) Rh/Zr0.50Ce0.40La0.05Nd0.05 48 347 — (1:1) (30g) + Pt/ Oxide (30 g) + Pt/ Ce0.60Zr0.30Y0.10 Ce0.60Zr0.30Y0.10 Oxide(30 g) + theta- Oxide (60 g) + Pt- alumina (80 g) Rh/theta-alumina (70g) Example La01.00Fe0.95Pd0.05o3/ La1.00Fb0.95Rh0.05o3/ 0.70 0.20 0.2040 — 374 RC-15 Ba-theta-alumina (Ba: 4%) theta-alumina (1:3) (38 g) +Pt/ 48 361 — (1:4) (46 g) + Pt/ Ce0.60Zr0.30Y0.10 Ce0.60Zr0.30Y0.10Oxide (60 g) Oxide (45 g) Example La01.00Fe0.95Pd0.05o3/La0.90Ca0.10Fe0.90Pt0.10o3/ 0.70 0.35 0.50 40 — 363 RC-16 theta-alumina(2:3) (40 g) + Pt/ theta-alumina (2:3) (3:2 g) + Pt- 48 335 —Ce0.60Zr0.30Y0.10 Rh/Zr0.70Ce0.25La0.02Nd0.03 Oxide (30 g) + theta-Oxide (40 g) + Pt/ alumina (80 g) Ce0.60Zr0.30Y0.10 Oxide (60 g)Comparative La1.00Fe0.95Pd0.05o3/gamma- PT-Rh/Ce0.30Zr0.70o2 (50 g) +gamma- 1.00 0.66 0.50 48 — >500   Example alumina (1:1) (60 g) + gamma-alumina (30 g) 432 — RX-13 alumina (30 g)

While the illustrative embodiments and examples of the present inventionare provided in the above description, such is for illustrative purposeonly and it is not to be construed restrictively. Modification andvariation of the present invention which will be obvious to thoseskilled in the art is to be covered in the following claims.

INDUSTRIAL APPLICABILITY

Thus, the exhaust gas purifying catalyst of the present invention canmaintain the catalytic activity of the noble metal at a high level overa long time and achieve satisfactory emission control performance, evenin an atmosphere of high temperature exceeding 900° C. to 1000° C. Itcan be advantageously used as an exhaust gas purifying catalyst forautomobiles.

1. An exhaust gas purifying catalyst comprising a noble metal, aperovskite-type composite oxide, theta-alumina and/or alpha-alumina. 2.The exhaust gas purifying catalyst according to claim 1, which comprisesa perovskite-type composite oxide containing a noble metal,theta-alumina and/or alpha-alumina.
 3. The exhaust gas purifyingcatalyst according to claim 2, wherein the perovskite-type compositeoxide containing a noble metal is supported by theta-alumina and/oralpha-alumina.
 4. The exhaust gas purifying catalyst according to claim2, wherein the perovskite-type composite oxide containing a noble metalis supported by at least one thermostable oxide selected from the groupconsisting of zirconia composite oxides represented by the followinggeneral formula (1), ceria composite oxides represented by the followinggeneral formula (2), SrZrO₃ and LaAlO₃:Zr_(1−(a+b))Ce_(a)R_(b)O_(2−c)  (1) wherein R represents alkaline earthmetals and/or rare-earth elements excluding Ce; a represents an atomicratio of Ce satisfying the following relation: 0.1≦a≦0.65; b representsan atomic ratio of R satisfying the following relation: 0≦b≦0.55;[1−(a+b)] represents an atomic ratio of Zr satisfying the followingrelation: 0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect,Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (2) wherein L represents alkaline earthmetals and/or rare-earth elements excluding Ce; d represents an atomicratio of Zr satisfying the following relation: 0.2≦d≦0.7; e representsan atomic ratio of L satisfying the following relation: 0≦e≦0.2;[1−(d+e)] represents an atomic ratio of Ce satisfying the followingrelation: 0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.
 5. Theexhaust gas purifying catalyst according to claim 3, whereintheta-alumina and/or alpha-alumina supporting the perovskite-typecomposite oxide containing a noble metal, or the thermostable oxidesupporting the perovskite-type composite oxide containing a noble metalis prepared by incorporating theta-alumina and/or alpha-alumina, or athermostable oxide into a pre-crystallization composition before thecrystallization of the perovskite-type composite oxide containing anoble metal, in the production of the perovskite-type composite oxidecontaining a noble metal.
 6. The exhaust gas purifying catalystaccording to claim 3, which further comprises at least one thermostableoxide selected from the group consisting of zirconia composite oxidesrepresented by the following general formula (1), ceria composite oxidesrepresented by the following general formula (2), theta-alumina,alpha-alumina, gamma-alumina, SrZrO₃ and LaAlO₃:Zr_(1−(a+b))Ce_(a)R_(b)O_(2−c)  (1) wherein R represents alkaline earthmetals and/or rare-earth elements excluding Ce; a represents an atomicratio of Ce satisfying the following relation: 0.1≦a≦0.65; b representsan atomic ratio of R satisfying the following relation: 0≦b≦0.55;[1−(a+b)] represents an atomic ratio of Zr satisfying the followingrelation: 0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect,Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (2) wherein L represents alkaline earthmetals and/or rare-earth elements excluding Ce; d represents an atomicratio of Zr satisfying the following relation: 0.2≦d≦0.7; e representsan atomic ratio of L satisfying the following relation: 0≦e≦0.2;[1−(d+e)] represents an atomic ratio of Ce satisfying the followingrelation: 0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.
 7. Theexhaust gas purifying catalyst according to claim 2, wherein theperovskite-type composite oxide containing a noble metal is mixed withtheta-alumina and/or alpha-alumina.
 8. The exhaust gas purifyingcatalyst according to claim 7, wherein at least one thermostable oxideselected from the group consisting of zirconia composite oxidesrepresented by the following general formula (1), ceria composite oxidesrepresented by the following general formula (2), gamma-alumina, SrZrO₃and LaAlO₃ is further mixed:Zr_(1−(a+b))Ce_(a)R_(b)O_(2−c)  (1) wherein R represents alkaline earthmetals and/or rare-earth elements excluding Ce; a represents an atomicratio of Ce satisfying the following relation: 0.1≦a≦0.65; b representsan atomic ratio of R satisfying the following relation: 0≦b≦0.55;[1−(a+b)] represents an atomic ratio of Zr satisfying the followingrelation: 0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect,Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (2) wherein L represents alkaline earthmetals and/or rare-earth elements excluding Ce; d represents an atomicratio of Zr satisfying the following relation: 0.2≦d≦0.7; e representsan atomic ratio of L satisfying the following relation: 0≦e≦0.2;[1−(d+e)] represents an atomic ratio of Ce satisfying the followingrelation: 0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.
 9. Theexhaust gas purifying catalyst according to claim 2, wherein theperovskite-type composite oxide containing a noble metal is representedby the general formula (3):AB_(1−m)N_(m)O₃  (3) wherein A represents at least one element selectedfrom rare-earth elements and alkaline earth metals; B represents atleast one element selected from Al and transition elements excludingrare-earth elements and noble metals; N represents a noble metal; and mrepresents an atomic ratio of N satisfying the following relation:0<m<0.5.
 10. The exhaust gas purifying catalyst according to claim 9,wherein N in general formula (3) is at least one selected from the groupconsisting of Rh, Pd, and Pt.
 11. The exhaust gas purifying catalystaccording to claim 9, wherein the perovskite-type composite oxiderepresented by the general formula (3) is at least one selected from thegroup consisting of Rh-containing perovskite-type composite oxidesrepresented by the following general formula (4), Pd containingperovskite-type composite oxides represented by the following generalformula (5), and Pt containing perovskite-type composite oxidesrepresented by the following general formula (6):A_(1−p)A′_(p)B_(1−q)Rh_(q)O₃  (4) wherein A represents at least oneelement selected from La, Nd, and Y; A′ represents Ce and/or Pr; Brepresents at least one element selected from Fe, Mn, and Al; prepresents an atomic ratio of A satisfying the following relation:0≦p<0.5; and q represents an atomic ratio of Rh satisfying the followingrelation: 0<q≦0.8,AB_(1−r)PdrO₃  (5) wherein A represents at least one element selectedfrom La, Nd, and Y; B represents at least one element selected from Fe,Mn, and Al; and r represents an atomic ratio of Pd satisfying thefollowing relation: 0<r<0.5,A_(1-s)A′_(s)B_(1−t−u)B′_(t)Pt_(u)O₃  (6) wherein A represents at leastone element selected from La, Nd, and Y; A′ represents at least oneelement selected from Mg, Ca, Sr, Ba, and Ag; B represents at least oneelement selected from Fe, Mn, and Al; B′ represents at least one elementselected from Rh and Ru; s represents an atomic ratio of A′ satisfyingthe following relation: 0<s≦0.5; t represents an atomic ratio of B′satisfying the following relation: 0≦t<0.5; and u represents an atomicratio of Pt satisfying the following relation: 0<u≦0.5.
 12. The exhaustgas purifying catalyst according to claim 1, wherein the theta-aluminaand/or alpha-alumina is represented by the following general formula(7): (Al_(1−g)D_(g))₂O₃  (7) wherein D represents La and/or Ba; and grepresents an atomic ratio of D satisfying the following relation:0≦g≦0.5.
 13. The exhaust gas purifying catalyst according to claim 6,wherein the zirconia composite oxide comprises a zirconia compositeoxide supporting Pt and/or Rh, the ceria composite oxide comprises aceria composite oxide supporting Pt, the theta-alumina comprises atheta-alumina supporting Pt and/or Rh, and the gamma-alumina comprises agamma-alumina supporting Pt and/or Rh.
 14. The exhaust gas purifyingcatalyst according to claim 1, which comprises a coating layer supportedby a catalyst carrier, the coating layer includes an outer layerconstituting its surface layer, and an inner layer arranged inside theouter layer, and the outer layer and/or the inner layer comprises bothat least one of theta-alumina and alpha-alumina, and the perovskite-typecomposite oxide containing a noble metal.
 15. The exhaust gas purifyingcatalyst according to claim 14, wherein the inner layer comprisestheta-alumina and/or alpha-alumina each supporting the perovskite-typecomposite oxide containing a noble metal.
 16. The exhaust gas purifyingcatalyst according to claim 14, wherein the inner layer comprises thethermostable oxide supporting the perovskite-type composite oxidecontaining a noble metal.
 17. The exhaust gas purifying catalystaccording to claim 14, wherein the inner layer comprises the Pdcontaining perovskite-type composite oxide.
 18. The exhaust gaspurifying catalyst according to claim 14, wherein the outer layercomprises the Rh-containing perovskite-type composite oxide.
 19. Theexhaust gas purifying catalyst according to claim 14, wherein the Ptcontaining perovskite-type composite oxide is contained in the innerlayer and/or the outer layer.
 20. The exhaust gas purifying catalystaccording to claim 0.14, wherein the noble metal contained in the outerlayer is Rh and/or Pt, and the noble metal contained in the inner layeris at least Pd.
 21. The exhaust gas purifying catalyst according toclaim 14, wherein the inner layer comprises the ceria composite oxidesupporting theta-alumina and Pt, and the outer layer comprises at leastone thermostable oxide selected from the group consisting of thezirconia composite oxide supporting Pt and Rh, the ceria composite oxidesupporting Pt, and theta-alumina supporting Pt and Rh.
 22. The exhaustgas purifying catalyst according to claim 1, which further comprisessulfates, carbonates, nitrates, and/or acetates of Ba, Ca, Sr, Mg, orLa.
 23. A catalyst composition comprising a noble metal, aperovskite-type composite oxide, theta-alumina and/or alpha-alumina.